as automatic ice maker according to the present invention will now be explained with reference to the attached drawings . according to the present invention , an elongated stop arm 11 in the form of a triangular plate is used as shown in fig1 to fig3 instead of using the stop arm in the form of a wire as in the conventional automatic ice maker . the distal end of the stop arm 11 is supported through a coil spring 13 rotatably by a driving shaft 12 projected from the bottom surface of a control box 5 so that the stop arm 11 can be rotated with respect to the driving shaft 12 against the force of the coil spring 13 when the stop arm 11 is hit against an obstacle . as shown in fig4 and fig5 a rod shaped cam follower 16 is provided on the driving shaft 12 so as to extend radially therefrom so that the tip end of the cam follower 16 is brought into contact with a cam surface of a cam 15 fixed to an output shaft 14 to be rotated by a motor . the configuration of the cam surface of the cam 15 is so determined that the stop arm 11 is positioned below the tray 1 when the heater is energized and that the stop arm 11 swings horizontally on the bin 8 according to the rotation of the ejector fingers 4 when the heater is not energized . a magnet 17 is mounted on the tip end of an arm extending radially from the driving shaft 12 , and an arm hole ic 19 is provided on a base plate 18 of the control box 5 facing the magnet 17 with a gap therebetween . a magnet 20 is mounted on an end surface of the output shaft 14 , and an original point hole ic 21 is provided on the base plate 18 facing the magnet 20 with a gap therebetween . according to the automatic ice maker of the present invention , the stop arm 11 is positioned below the tray 1 directly before or directly after the energization of the heater , or at the same time of the energization of the heater , after the water in the tray 1 has been frozen , so that the ice cubes in the bin 8 is prevented from being molten by the heat radiation from the heater . fig5 shows a state that the stop arm 11 is positioned above the bin 8 and outside of the tray 1 , the arm hole ic 19 is turned off , the original point hole ic 21 is turned on , the water in the tray 1 is frozen , the thermostat is turned on , and the heater is energized , but the ejector fingers 4 are not yet rotated . fig6 shows a state after about 90 seconds from the energization of the heater . the stop arm 11 is not yet moved to the below the tray 1 . the arm hole ic 19 and the original point hole ic 21 are turned off , and the ejector fingers 4 are rotated by 15 °. fig7 shows a state that the stop arm 11 is swing and positioned below the tray 1 , the ejector fingers 4 are rotated by 195 °, the arm hole ic 19 is turned on , and the original point hole ic 21 is turned off . in this state , the ice cubes stored in the bin 8 are prevented from being molten by the heat radiation from the heater , because the stop arm 11 is positioned below the tray 1 . fig8 shows a state that the stop arm 11 is not yet moved from below the tray 1 to the outside , but the ejector fingers 4 are rotated by 270 °, the arm hole ic 19 is turned on , and the original point hole ic 21 is turned off . fig9 shows a state that the stop arm 11 is not yet moved from below the tray 1 to the outside , but the ejector fingers 4 are rotated by 300 °, the arm hole ic 19 is turned on , and the original point hole ic 21 is turned off . fig1 shows a state that the stop arm 11 is swung and moved from below the tray 1 to the outside , the ejector fingers 4 are rotated by 330 °, and the arm hole ic 19 and the original point hole ic 21 are turned off . fig1 shows a state that the stop arm 11 is positioned at the outside of the tray 1 , the ejector fingers 4 are returned to the original position , the arm hole ic 19 is turned off , and the original point hole ic 21 is turned on . fig1 shows a cross section of the stop arm 11 . the upper surface of the stop arm 11 is inclined downwards gradually from the side of the tray 1 to the opposite side , so that the ice tips or water drops formed by the ejecting operation of the ejector fingers 4 are removed automatically when they are fallen on the stop arm 11 . further , conventionally , either one of n and s poles of the conventional single magnet is used as the magnet 17 or 20 for the hole ic . in this case , however , the relation between the relative distance and the magnetic flux density of the original point hole ic 21 and the magnet 20 is shown by a gentle curve as shown in fig1 . the original point hole ic 21 is operated only when the distance between the original point hole ic 21 and the magnet 20 is changed to the large extent and the change of the magnetic flux density becomes a predetermined value , so that the precision of the operation of the original point hole ic 21 is deteriorated . accordingly , in the present invention , a magnet consisting of superposed n and s poles as shown in fig1 is used as the magnet 20 . in this case , the relation between the relative distance and the magnetic flux density of the original point hole ic 21 and the magnet 20 is shown by a curve having a sharply inclined portion as shown in fig1 . accordingly , the original point hole ic 21 can be operated by a small change in distance if the above sharply inclined portion of the curve is used , so that the precision of the operation of the original point hole ic 21 can be enhanced . as stated above , according to the present invention , the original point of rotation of the ejector fingers 4 can be detected by the original point hole ic 21 , and the stop arm 11 can be swung according to the output of the arm hole ic 19 only when the output shaft 14 is in the angular position between 15 ° to 330 °. further , the stop arm 11 can be prevented from being damaged . the ice cubes can be prevented from being molten by the heat radiation from the heater , because the stop arm 11 can be positioned below the bottom surface of the tray 1 . furthermore , the operations of the ejector fingers 4 and the stop arm 11 can be controlled precisely by elevating the sensitivity of the original point hole ic 21 . it should be understood that many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof . the scope of these changes will become apparent from the attached claims .