referring to fig1 which shows a first embodiment of the present invention , reference numeral 1 designates a camera body and reference numeral 2 denotes a motor drive device removably mountable to the camera body 1 . electrical connection between the camera body 1 and the motor drive device 2 is made by electrical contacts a - f . designated by 3 is a power source within the camera body 1 . when the motor drive device 2 is mounted to the camera body 1 , a power source change - over switch s 1 is changed over from s 1b to s 1a by an automatic change - over mechanism , not shown . the circuit of the camera body 1 is supplied with power from the power source 34 of the motor drive device 2 which will hereinafter be described . a metering switch s 2 is closed when the unshown shutter button of the camera body 2 is depressed a step without the motor drive device 2 being mounted to the camera body . transistors 5 , 8 and 9 are designed such that a conduction signal is applied thereto through a reverse current blocking diode 4 upon closing of the switch s 2 , whereupon these transistors are rendered conductive . a control circuit 11 is supplied with power upon conduction of the transistor 9 . the control circuit 11 includes a metering circuit , an exposure control circuit , a sequence control circuit , an indication circuit , a shutter control and aperture control electromagnet , a release electromagnet , etc . even if the depression of the shutter button is released and the metering switch s 2 is opened , the conduction of the transistor 8 is continued for a predetermined time , say , 30 seconds , with the aid of a capacitor 6 and a resistor 7 . a transistor 12 is rendered conductive when the camera has entered an operation effecting exposure control such as shutter control , and during the exposure control operation , the transistor 12 ensures power supply to the control circuit 11 independently of the off position of the metering switch s 2 . a release switch s 3 is closed with the metering switch s 2 when the unshown shutter button of the camera body 1 is further depressed from its one - step depressed position , thereby releasing the shutter of the camera body . a motor driving switch s 4 is closed when the exposure of the camera is completed with the shutter closed , and is opened when shutter charge and film advance is completed . during its on condition , the switch s 4 transmits to the motor drive device a motor driving signal for film advance . in the motor drive device 2 , a metering switch s 6 is closed when the unshown shutter button of the motor drive device is depressed a step . a power supply control transistor 29 has applied thereto a conduction signal through a reverse current blocking diode 36 upon closing of a switch s 6 and is thereby rendered conductive to operate a constant voltage circuit 35 . the circuit 35 supplies a predetermined constant voltage to the camera body 1 and also supplies a constant voltage to the circuit of the motor drive device . this constant voltage circuit 35 puts out a predetermined voltage lower than the output voltage of a power source 34 . by the closure of the metering switch s 6 being transmitted to the camera body through a contact c , the power supply transistor 9 for the camera has applied thereto a conduction signal as previously described and is thereby rendered conductive to effect the power supply to the control circuit 11 within the camera body . even if the metering switch s 6 is opened , the transistor 9 is turned on for a predetermined time determined by the aforementioned capacitor 6 , resistor 7 and transistor 8 . the on signal of the transistor 9 turns on a transistor 24 through a resistor 10 . by the conduction of the transistor 24 , the transistor 29 is also rendered conductive to continue the power supply to the constant voltage circuit 35 and the control circuit 11 . when a wind - up mode switch s 8 is in its on position , the automatic film wind - up mode by the motor is brought about and , when the switch s 8 is in its off position , there is brought about the manual film wind - up mode in which the motor is not rotated but film wind - up is effected by means of an unshown wind - up lever on the camera body . at this time , shutter release is effected only by means of the shutter button of the camera body . this manual operation mode is used during loading of a film , or when it is not desired to have any drive sound produced by motor wind - up , or when the voltage of the battery is insufficient to drive the motor but sufficient to drive the camera . the operation when the switch s 8 is in its on position is effected in the following manner . when the unshown shutter button of the motor drive device is further depressed from its one - step depressed position , the release switch s 5 is closed with the metering switch s 6 and if , at that time , the potential of the capacitor c 1 of a release timing circuit comprising a capacitor c 1 , a resistor , a comparator 14 and a transistor 13 is higher than the comparison reference voltage of the comparator 14 , transistor 13 is rendered conductive and a release signal is put out to the camera body 1 , whereupon exposure of the film within the camera is started . when the exposure is completed , the motor driving switch s 4 is closed . if , at that time , a photography mode switch s 7 is in its off position , the capacitor c 1 is not discharged by the switch s 4 and therefore , the capacitor c 1 is not reset and accordingly , the on state of transistor 13 does not change even if the release switch s 5 remains closed . consequently , even when wind - up is completed , re - release does not take place . for rephotography , the hand is released from the shutter button and the release switch s 5 is once opened , whereafter the release switch s 5 is again closed and the shutter is released . that is , this mode is a one - frame photography mode . when the photography mode switch s 7 is in its on position , if the motor driving switch s 4 is closed , the capacitor c 1 is discharged through the reverse current blocking diode and the comparator 14 is inverted . transistor 13 once changes from its on state to its off state even if the release switch s 5 is in its on position . when wind - up is completed and the switch s 4 is opened , the comparator is inverted at a predetermined timing after that point of time and if , at that time , the release switch s 5 is in its on position , the transistor 13 is again rendered conductive and re - release takes place . that is , this mode is a continuous photography mode . as soon as the motor driving switch s 4 is closed , transistor 15 is also turned on . accordingly , transistor 19 is also turned on and power is supplied to a relay coil 31 . thereby , a relay switch 32 is changed over to rotate a motor 33 , whereby the film within the camera body is wound up through a wind - up mechanism , not shown . simultaneously with the conduction of the transistor 15 , integration of an end timer comprising a resistor , a capacitor c 2 and a comparator 17 is started , but during the usual wind - up time , the integration potential of the capacitor c 2 does not reach the inversion potential of the comparator 17 . accordingly , the output of the comparator 17 remains high and does not affect the operation of transistor 19 . transistor 16 is for rapidly discharging the capacitor c 2 and resetting the same when the transistor 15 has been turned off by completion of wind - up . to prevent the motor from being burnt when the power supply time of the motor has become longer than a predetermined time , namely , when the film at its end has become incapable of being drawn out from the film magazine , or when the voltage of the battery has dropped and the wind - up time has become longer , or when film wind - up has become impossible for some reason , the comparator 17 is inverted . then , the output thereof become low and transistor 19 is turned off through a reverse current blocking diode 18 and the motor 33 is stopped . also , when the output of the comparator 17 becomes low , led 30 is turned on through a reverse current blocking diode 20 , indicating the stoppage of the motor . the low output of the comparator 17 renders a power supply transistor 29 conductive through a reverse current blocking diode 21 , so that a timer composed of the capacitor 6 and the resistor 7 on the camera body side becomes off and this signal is transmitted through resistor 10 to transistor 24 and , even if this transistor is turned off , the power supply to the comparator 17 is continued through the constant voltage circuit 35 and thus , the motor stoppage indication by led 30 is maintained . this indication is used as the warning when the motor power supply time has become longer than a predetermined time . when a battery check switch s 9 is closed , a dummy current having a value substantially equal to that of the current flowing to the motor 33 flows to a dummy resistor 26 and at the same time , transistor 24 is turned on through a reverse current blocking diode 25 . consequently , a conduction signal is applied to a power supply transistor 29 , which is thus turned on , and the constant voltage circuit 35 is operated . the output voltage of this circuit 35 is divided by resistors 37 and 38 and the divisional voltage is applied as a comparison reference voltage to a battery check comparator 22 . the output of the circuit 35 also acts to operate the comparator 22 . the voltage of a battery 34 is divided by resistors 27 and 28 and applied to the other input of the comparator and , when that voltage is higher than the comparison reference voltage , namely , when the voltage of the battery 34 is higher than a predetermined voltage , the output of the comparator 22 becomes low and a current flows to led 30 , which thus indicates that the voltage is sufficient . when the voltage of the battery is below the predetermined voltage , the output of the comparator 22 becomes high and led 30 is turned off . whenever a battery check switch s 9 is off , the output of the comparator 22 is high and therefore , the turn - on of led 30 by the comparator 22 does not occur . even if the battery check switch s 9 is closed and transistor 24 is turned on and the power supply transistor 29 becomes conductive , the conduction signal is prevented by a reverse current blocking diode 36 from being transmitted to the camera body side and therefore , the power supply circuit 5 , 8 , 9 on the camera body side is not closed by the closing of the battery check switch s 9 . that is , when the metering switch s 6 is closed , the power supply circuit 5 , 8 , 9 on the camera body side is closed , but when the battery check switch s 9 is closed , the power supply circuit 5 , 8 , 9 on the camera body side is not closed . the comparator 22 and resistors 27 , 28 , 37 , 38 together constitute a discriminating circuit for discriminating whether the output voltage of the power source 34 is above a predetermined level . fig2 shows a second embodiment of the present invention , and particularly shows portions of the second embodiment which differ from the first embodiment . the second embodiment does not employ the reverse current blocking diode 36 shown in the first embodiment . in the second embodiment , a second power supply transistor 39 is parallel - connected to the power supply transistor 29 . the first power supply transistor 29 is controlled only by metering switches s 6 and s 2 , and the second power supply transistor 39 is controlled only by transistor 24 and comparator 17 . in the other points , the construction of the present embodiment is the same as that of the first embodiment and therefore need not be described further . the motor driven camera hitherto described comprises a camera body and a motor drive device mountable to the camera body . however , the motor driven camera of the present invention includes the type which contains a motor drive device in the camera body . as has been hitherto described , according to the present invention , in a motor driven camera wherein a power source for driving a motor is connected to another electric circuit through a constant voltage circuit , the output of the constant voltage circuit is used as the reference voltage for checking the voltage of the power source , and this leads to a simplified construction of the battery checking device .