Abstract: A high-pressure and low-pressure selecting valve includes a valve body and a valve member movably provided in the valve body. The valve body has a pair of input ports, at least one output port, and a low-pressure port. The input ports, the output port, and the low-pressure port are so formed that when input to one of the input ports is of a higher hydraulic pressure, the valve member is moved by the pressure to connect the one input port to one of the output ports and the other input port to the low-pressure port. A swash-plate type hydraulic motor system selects, by means of this valve, high-pressure liquid necessary for controlling the swash plate and simultaneously connects the low-pressure relief valve to the low-pressure side of the system.