Disclosed is an engine of a personal watercraft having a water jet pump at a rear end thereof, in which a center of gravity of the engine is located rearward for improvement of planing capability of the watercraft. The engine comprises: a crankcase having a front end wall and a rear end wall; a crankshaft provided inside the crankcase; a generator provided at an output end portion of the crankshaft, the generator including a rotor fixed to the crankshaft; a starter motor provided on an output end side of the crankshaft outside the crankcase; and a clutch provided between the starter motor and the rotor of the generator, for connecting/disconnecting the starter motor to/from the rotor.