Abstract: A charge pump for a hydrostatic transmission, having a self-charge relief function, in which a first toothed wheel, a second toothed wheel, and a pump casing, housing therein the first and second toothed wheels, are molded of heat resistant resin material, thereby reducing the weight of the charge pump, stabilizing its charge relief function and reducing the wear of the lower surface of a center section.Check valves are housed in the pump casing so that operating oil sealed between a hydraulic pump and a hydraulic motor can always be kept in a proper amount, regardless of whether the charge pump is driven or not.