To prevent a noise from being generated from a chain tensioner just before the stop of an engine in the constitution for transmitting the rotating drive force of a starting motor to the engine through a chain.

The torque command value of the starting motor is changed from zero to a target torque value Tmbstop while the engine speed Nen (rpm) falls from Nen0 to Nen1 on the basis of a request of engine stop, kept at the target torque value Tmbstop up to Ne2, and then returned from the target torque value Tmbstop to 0 from Nen2 to the stopping. The torque of the starting motor is worked in the reverse direction to the rotating direction of the engine according to the torque command value, whereby the rotating fluctuation just before engine stop is suppressed to suppress the tension change of the chain.