A suck-back valve having an open/close valve with a suck-back function is provided. The suck-back valve includes a suck-back chamber formed in a valve internal channel of the open/close valve, a piston shaft portion that connects the piston main body and an open/close pressuring member that moves in the suck-back chamber in the axial direction to apply pressure to a valve piece, bellows that accommodate the piston shaft portion inside, separating an actuator from the valve internal channel, and that are connected to the open/close pressuring member at one end and are supported by a casing at the other end, wherein a two-step operation is carried out at the time of the closing operation of the valve piece, including a valve closing operation step in which the piston shaft portion, along with the piston main body and the open/close pressuring member, moves to the fully closed position of the valve piece, and a suck-back operation step in which the piston shaft portion and the open/close pressuring member further move from the fully closed position of the valve piece so as to increase the volume of the suck-back chamber.