Object of the present invention is a start-up once the jam state, fundamentally blocks the supply of power to the starter motor By preventing damage to the starter motor to prevent damage of the starter motor driven concurrent rewrite of the starting key switch device of the engine to provide. Means of the present application devised for achieving the above object is achieved And the starter motor, in the engine start-up device consisting of a battery power supply and start-key switch mechanism, Rotation detection sensor for detecting the rotation of the timing belt and; And the short-circuit switch circuit consisting of the ignition key switch and the series circuit; Solenoid and for turning on and off the short-circuit switches the circuit; And When the timing signal output from the belt rotation detection sensor and an electronic control unit that controls to switch by operating the solenoid to a circuit off the short-circuit switch position; The features that are configured to include.