PURPOSE: To reduce number of the parts used, compact the whole construction, facilitate fabrication and to suppress the cost, by supplying the pressure fluid discharged selectively by two pumps, to the power steering device from a high pressure chamber formed in the middle of the two pumps.

CONSTITUTION: When a small-capacity pump P1 is driven by a drive shaft 8, the fluid in a reserver tank 56 is taken in the small-capacity pump P1 from a suction pipe 17 to be discharged in the form of pressure fluid, which then flows into a high pressure chamber 18 formed between two pressure plates 6, 12. A large-capacity pump P2 is driven by a drive shaft 9 when an electromagnetic clutch 2 is put in engagement, and the fluid discharged therefrom converges at said high pressure chamber 18 with the fluid discharged by the small-capacity pump P1. While the car is running at extra-low speed, both pumps P1, P2 are driven, and the combined flow from two pumps is fed to the power steering device PS from a feed port 39. When the car speed increases thereafter, the large-capacity pump P2 stops rotating, while the small-capacity pump P1 is solely driven in continuity.