spring 9 so that the lock member 8 is rotated clockwise an engaging plate 14 is fixedly mounted on the on vehicle apparatus 4 by suitable means such as screws 15 while the electromagnetic actuator m is not energized the claw 3 enters an engaging slot 13 and its tip extends into and passes through the slot to engage with it when apparatus 4 is housed in the case 1 a connector 16 mounted on the apparatus 4 is coupled to a connector 17 mounted on the case 1 to thereby obtain electrical connection therebetween referring to fig4 voltage from a power supply 21 is applied to a time constant circuit 22 via an off contact of an vehicle engine switch 20 an output from the time constant circuit 22 is supplied to a solenoid driver 23 to energize the solenoid 11 and drive the plunger 12 for a time period determined by the time constant circuit 22 after a movable contact of the engine switch 20 is moved to the off contact the solenoid 11 maintains de energized at the off contact of the engine switch 20 except when the engine switch 20 is at an ignition on state and for the period determined by the time contact circuit 22 therefore during the de energized period of the solenoid 11 as shown in fig2 the lock member 8 takes a position rotated counter clockwise with respect to fig3 by the force of the coil spring 9 the claw 3 enters the engaging slot 13 and the.