PURPOSE: To facilitate the change for retention of constant speed driving and for accelerated or decelerated driving, by providing a retaining electromagnet and a releasing electromagnet.

CONSTITUTION: When a main switch is set, the retaining electromagnet SM is actuated, so that a movable contact 11 is pulled, a locking shaft 5 is advanced by link mechanisms 9, 12, and a wire 23 is clamped and retained between a push plate 7 and the locking shaft 5. As a result, the opening of the accelerator can be kept at a state under this restraining operation to keep the automobile driving at constant speed. When it is required to decelerate, a brake pedal is operated, thereby the releasing electromagnet RM is actuated, an end 13b of the third lever is withdrawn, a swingable arm 13a is rotated about a stationary contact 15, the movable contact 11 is pushed out, and therefore the locking shaft 5 releases the retenion of the pulling wire 23 with an aid of energy in a spring 18. When it is required to accelerate, an accelerator pedal is operated, thereby the releasing electromagnet RM is actuated, and the locking shaft 5 releases the retention of the pulling wire 23 to permit the acceleration.