Abstract: A flow control valve having a bypass valve section that opens when a main valve section has approached a closed state has a bypass start point that can be easily varied and adjusted, even after installation of the flow control valve. Further, cavitation is not generated in the valve. The flow control valve comprises a cylindrical body having a bypass valve seat and a plurality of protrusions on an inner peripheral surface to form bypass flow passages therebetween. A bypass opening and closing body has a bypass valve element formed at its front end portion and a plurality of slit holes formed on its outer peripheral surface so as to open and close the bypass flow passages between the respective protrusions, and is disposed in an axially movable manner. A piston is disposed in an axially movable manner in the bypass opening and closing body and has an enlarged outer diameter section formed on its rear portion and a communication hole penetrating therethrough in the axial direction.