some preferred embodiments according to the present invention will be described with reference to fig1 through 6 , in which fig1 and 2 show a structure of the rotary handle ; fig3 ( a ) and 3 ( b ) show a development of an alternate operation type cam mechanism provided in a handle lock lever ; fig4 is a plan view of a handle cover ; fig5 shows a structure of a door lock lever provided on the back surface of the handle cover ; and fig6 shows an overall structure of an external operation handle device combined with a circuit breaker . the same members in the embodiment are given the same symbols as in fig7 through 10 and description is omitted . the external operation handle device shown in fig6 has basically a similar structure to the conventional structure as shown in fig7 and 8 . nevertheless , the rotary handle 4 of the embodiment shown in fig6 comprises a newly added cam mechanism 15 of an alternate operation type , details of which will be described hereinafter . further , in an inner periphery of an opening on a top surface of a handle cover 7 mounting the rotary handle 4 ( see fig4 ), locking notches 19 a , 19 b , and 19 c are formed corresponding to open position for unlocking a door panel as well as on and off positions of the rotary handle 4 , the lock notches being provided for anchoring and holding a handle lock lever 8 at the respective pull out positions . the following describes details of the structure and operation of these parts . firstly , referring to fig1 and fig2 , the grip portion of the rotary handle 4 includes a handle lock lever 8 that can be pulled out and pushed in , in the direction indicated by the allow p . the handle lock lever 8 is guided and supported through a guide pin 8 b on the rotary handle 4 . the handle lock lever 8 has a hole 8 a for hanging a padlock at the outer end and an anchor rib 8 c formed at the bottom of the handle lock lever 8 for anchoring and holding the handle lock lever 8 on the handle cover 7 . the anchor rib 8 c projects downward through a clearance groove 4 b - 1 in the radial direction cut in a disk - shaped flange part 4 b of the rotary handle 4 . a cam mechanism 15 of an alternate operation type is constructed in the rotary handle 4 as described hereinafter . the cam mechanism 15 consists of a groove cam with steps 16 carved on the side face of the handle lock lever 8 , a control bar 17 having an l - shaped bend at its tip to slide on the cam surface of the groove cam 16 , and an urging spring 18 ( a compression spring ) for pushing the handle lock lever 8 towards the pull - out direction . the control bar 17 is a wire spring having an l - shaped bend ( in an acute angle ) at one end thereof and a c - shaped bend at the other end thereof , the latter being pushed into and held at a holder groove 4 c in a slit shape formed in the rotary handle 4 . fig3 ( a ) and 3 ( b ) show a detailed configuration of the groove cam 16 with steps . the groove cam 16 has a cam pathway with a heart shape starting at a part a , through parts b , c , d , e , f , g , and h , and returning to the part a , as shown in fig3 ( a ). at the locations of corners along the pathway , formed are steps b , d , f , and h that have a ratchet shape and exhibit unidirectional ( backstop ) property . when the handle lock lever 8 , which includes the cam mechanism 15 having the above - described construction , is stored in the rotary handle 4 , the hook of the control bar 17 stays at e in the cam pathway in fig3 ( a ) and 3 ( b ); this position is referred to as a waiting position p 1 . from this state , when the outer end of the handle lock lever 8 is pushed by a finger towards the interior of the rotary handle 4 ( first push operation ), the hook of the control bar 17 slides beyond the slope of the step f moving into position g . ( reverse motion from e to c is obstructed by the step d .) leaving the finger off the handle lock lever 8 at this state , the lock lever slides towards the pulling out direction receiving a spring force of the urging spring 18 . during this sliding process , the hook of the control bar 17 moves from the position g and slides beyond the slope of the step h moving into position a , which is referred to as a lock position p 2 . in this state , the outer end of the handle lock lever 8 is projecting out from the periphery of the rotary handle 4 . from this state , when the handle lock lever 8 is pushed inward again ( second push operation ), the hook of the control lever 17 slides beyond the slope of the step b moving into position c . ( reverse motion from a to g is obstructed by the step h .) leaving the finger off the handle lock lever 8 , the lock lever is pushed back by receiving the spring force of the urging spring 18 . in this moving back process , the hook of the control lever 17 slides from the position c , over the slope of the step d , and back to the position e ( the waiting position p 1 ). thus , the handle lock lever 8 returns to the initial waiting position . relating to the handle lock mechanism described previously , locking notches are formed on the top surface of the handle cover , which receives and supports the rotary handle 4 , as describe below . referring to fig4 , locking notches 19 a , 19 b , and 19 c are formed by partially cutting off the inner periphery of an opening on the top surface of the handle cover 7 corresponding to the on , off , and open positions , respectively , of the rotary handle 4 , for anchoring and holding ( inhibiting rotational motion ) the anchor rib 8 c of the handle lock lever 8 projecting out of the rotary handle 4 . the depths of the locking notches 19 a and 19 b corresponding to the on and off positions are large because a padlock is hung on the handle lock lever 8 at the on and off positions of the rotary handle as mentioned referring to fig1 . at the open position , on the other hand , a padlock does not need to be hung on the handle lock lever 8 , so the locking notch 19 c is designed to be shallow . in a door lock mechanism shown in fig5 of the embodiment , a door lock lever 9 is pivotally supported by a support pin 9 a like the conventional structure of fig1 and the lever cam portion of the door lock lever 9 is arranged to project into the moving path of a protrusion 5 b of the turn base 5 connected to the handle shaft 4 a . the door lock lever 9 is not provided with a leaf spring 13 for self supporting in the conventional structure ( see fig1 ). instead , an urging spring 20 , a tension coil spring , is provided to urge the door lock lever 9 towards the locking direction . the following describes an operation of an external operation handle device 2 having the above - described construction . to lock the rotary handle 4 at the on or off position , after turning the rotary handle 4 to the on or off position , the handle lock lever 8 is touched by a finger at its end and once pushed into the interior of the rotary handle 4 , and then released ( first push operation ). through this operation , the alternate operation of the cam mechanism 15 as described earlier referring to fig3 moves the handle lock lever 8 to the pulled out position and at the same time , the anchor rib 8 c engages with the locking notch 19 a or 19 b formed in the handle cover 7 to hold the handle lock lever 8 at this position inhibiting its rotation . in this state , a padlock 14 is hung on the handle lock lever 8 to lock the rotary handle 4 at the on or off position ( see fig1 ). to release lock of the rotary handle 4 , after removing the padlock 14 , the handle lock lever 8 is pushed at its end towards the interior of the rotary handle 4 and released ( second push operation ). through this operation , the handle lock lever 8 returns to the waiting position and is stored in the rotary handle 4 allowing the rotary handle to be turned . in order to open the door panel 10 of the switch board as shown in fig9 , the rotary handle 4 of the external operation handle device 2 is first turned to the off position to open the circuit breaker 1 . subsequently , the rotary handle 4 is further turned from the off position to the open position . through this operation , the protrusion 5 b of the turn base 5 in fig5 moves counterclockwise and pushes the cam portion of the door lock lever 9 . as a result , the door lock lever 9 rotates clockwise about the support pin 9 a and is released from the latch 12 a to unlock the door panel . when the rotary handle 4 is turned to the open position , the anchor rib 8 c of the handle lock lever 9 comes to face the locking notch 19 c shown in fig4 . pushing the handle lock lever 8 at this open position corresponding to the unlock operation for the door panel , the anchor rib 8 c engages with the locking notch 19 c through the alternate operation of the cam mechanism 15 and the handle lock lever 8 is anchored and held at this position . in this condition , the interlock has been released between the external operation handle device 2 and the door of the switch board , and the door lock lever 9 is held at the unlock position by itself without touching the rotary handle 4 , allowing the door panel 10 to be opened safely . in order to close and lock the door of the switch board , the opened door panel 10 is returned to the closed position and subsequently the handle lock lever 8 is pushed to return to the waiting position . then , the rotary handle 4 is moved back from the open position to the off position . through this operation , the door lock lever 9 is released from the self - holding condition at the unlock position and returns to the locked position receiving a spring force of the urging spring 20 , locking door of the switch board at the closed position . the disclosure of japanese patent application no . 2006 - 255923 filed on sep . 21 , 2006 is incorporated as a reference . while the invention has been explained with reference to the specific embodiments of the invention , the explanation is illustrative and the invention is limited only by the appended claims