PURPOSE: To enable to start an engine with ease and promptly, by providing a circuit connecting a battery, a magnet switch and a starting motor, and also providing a circuit having a throttle switch and a start detecting relay.

CONSTITUTION: When an ignition switch S1 is turned ON and a throttle grip is opened a little, a throttle switch S2 is turned ON. Resultantly, current from a battery B is passed to a third circuit 3 and a starter control relay RY1 is energized. On the other hand, a manget switch MS is energized by current passed to a second circuit 2. Further, current from the battery B is also passed to a first circuit 1, and a starting motor M is set into rotation. With such an arrangement, it is enabled to start an engine with ease and promptly without pressing a starter button.