A hydrostatic transmission constructed so that a check valve and a relief valve are made as compact as possible to supply oil to a closed circuit for connecting a hydraulic pump and a hydraulic motor, and to regulate maximum pressure in the closed circuit. A check valve and a relief valve are contained in a valve casing. A valve body of the relief valve is disposed opposite to a valve body of the check valve. A relief spring of the relief valve is retained by a cover detachably mounted to an open end of the valve casing, thereby facilitating pressure setting of the relief valve. The valve body of the relief valve is contained in a relief valve casing slidably disposed in the valve casing. A plunger, capable of urging the check valve in the opening direction via the relief valve casing, is provided in the cover, thereby enabling the check valve to be manually opened.