A marine propulsion device includes an engine, a cylinder cooling pathway through which a cooling water passes, a water pump, an electromagnetic valve, a water pressure sensor, a water temperature sensor, and a controller. The engine includes a cylinder. The cylinder cooling pathway is disposed in an area surrounding the cylinder. The water pump supplies the cooling water to the cylinder cooling pathway from outside. The electromagnetic valve restricts a flow of the cooling pathway in the cylinder cooling pathway. The water pressure sensor detects a water pressure of the cooling water in the cylinder cooling pathway. The water temperature sensor detects a water temperature of the cooling water in the cylinder cooling pathway. The controller is configured or programmed to control an opening degree of the electromagnetic valve based on a detection value of the water pressure sensor and a detection value of the water temperature sensor.