To prevent mixing of air into operating fluid in a operating fluid reservoir, and to use main components for both a pressurization type and a non-pressurization type in common.

This operating fluid reservoir 10 has an upper body 11 comprising a cylindrical base part 11a and a tube-like main part 11b above the base part 11a; and a circular casserole-like lower body 12 formed with partition part 24 surrounding an inner circumferential area of a flow straightening area and an outlet in a bottom part inside the partition part 24. The upper body 11 and the lower body 12 are connected with a strainer sandwiched. A base part of the upper body 11 is formed with the flow straightening area of an appropriate radial width along an appropriate range of an inner circumferential face, while the flow straightening area is formed with an appropriate number of flow deflection fins radially extending in appropriate circumferential positions, and an inlet 17 allowing inflow of operating fluid from an end of the flow straightening area to an tangential direction of the inner circumferential face. In the case of a pressurization type, the reservoir 10 also has a baffler 30 making the flow straightening area open to only an inner circumferential space of the partition part 24 of the lower body 12.