PURPOSE: To obtain simplified structure and reduced number of components for cutting of the cost by designing a combined use of propeller shaft bearing lubricant oil and hydraulic oil of a variable pitch propeller.

CONSTITUTION: Lubricant oil of front and rear bearings 4, 5 for supporting a propeller shaft 3 is supplied from a gravity tank 20, which also serves as a source of oil which is sent, so as to change the pitch of a variable pitch propeller, by a pump 15 in a hydraulic unit 14 through a switching valve 16 to a pitch control box 17 and then supplied through an oil pipe 18 in the propeller shaft to a servomotor piston 12 incorporated in a propeller hub 2. Such a combined use of the tank 20 permits combined uses of associated oil reservoir 21, pump 22 and other components.