A watercraft propulsion device includes an engine, a drive shaft, a propeller shaft, a rotational speed detector, and a controller. The drive shaft transmits power from the engine. The propeller shaft is rotationally driven by power transmitted from the drive shaft. The rotational speed detector detects an engine rotational speed. The controller executes a suppression control to suppress the engine rotational speed when a change rate of the engine rotational speed is equal to or larger than a prescribed value.