A forward rotation positioning operation of rotating a crankshaft in a forward direction is performed before start-up of an engine, and a reverse rotation start-up operation of rotating the crankshaft in a reverse direction is performed during the start-up of the engine. In the forward rotation positioning operation, a rotation driver drives the crankshaft such that a crank angle reaches a predetermined reverse starting range. In the reverse rotation start-up operation, the rotation driver drives the crankshaft such that the crank angle exceeds a predetermined start-up intake range from the reverse rotation starting range and reaches a predetermined start-up ignition range, a fuel injection device injects fuel such that a fuel-air mixture is introduced into a combustion chamber from an intake passage through an intake port, when the crank angle is in the start-up intake range, and an ignition device ignites when the crank angle is in the start-up ignition range. Ignition performed by the ignition device is prevented during the forward rotation positioning operation.