A manual opening/closing valve includes a manual handle, a valve element, a valve seat, an input port, and an output port. The manual opening/closing valve is arranged to move the valve element into contact with the valve seat when the manual handle is rotated, so that the valve is placed in a cutoff state in which communication between the input port and the output port is cut off, wherein the cutoff state includes a first cutoff state established when the manual handle is rotated to a first angle and a second cutoff state established when the manual handle is rotated to a second angle at which rotation operation force to the manual handle is converted to a cutoff load to be applied to the valve seat.