In a reservoir tank (5) of the present invention, a hydraulic fluid movement deterring wall (26) is disposed integrally with an upper half body (9) and extending toward a radial direction center of a cylindrical upper half body neck section (24) on a curved portion at a boundary between an inner peripheral surface (24a) of the cylindrical upper half body neck section (24) and an inner surface (25a1) of a ceiling portion (25a) of an upper half body trunk section (25) or on the inner peripheral surface (24a) of the upper half body neck section (24). The movement of the hydraulic fluid frontward (toward a hydraulic fluid inlet (10)) in a hydraulic fluid storage chamber 13 at a time when the reservoir tank (5) is tilted frontward is controlled by this hydraulic fluid movement deterring wall (26).