PURPOSE: To prevent atmosphere pollution and realize miniaturization and a light weight in the case of a small-sized hydrovehicle such as a jet propulsion type water ski by making the prime mover of an impeller an electric motor, utilizing part of high pressure water for jet to cool the electric motor and the heating portion of an electric system.

CONSTITUTION: An electric motor 8 is installed at a ship bottom portion, and an output shaft 9 is provided extendingly toward the rear, and a pump 11 having an impeller 10 is connected to the rear end, and is driven by means of the motor 8. By the drive of the pump 11, water is sucked from the ship bottom through a jet water passage 12 and made high pressure water, and a jet propulsion boat advances by conducting jetting toward the rear at a high speed through a ship nozzle 15. Also, a cooling water circulation portion 21 like a water jacket is provided at the outer periphery of the motor 8, and also a similar cooling water circulation portion 22 is provided at the outer periphery of a control unit 20. And, a cooling water pipe 23 is branched off from the discharge side of the pump 11, and part of high pressure water is made to become cooling water and supplied to cooling water circulation portions 21, 22, and the motor 8 and the control unit 20 are cooled. Cooling water is discharged through discharge openings 24a,24d.