A casing accommodates therein a movable valve adapted to be moved away from a valve seat by a hydraulic oil flowing through an oil-hydraulic circuit from a hydraulic cylinder to an oil-hydraulic pump. In an event of oscillatory hydraulic pressures in the hydraulic cylinder, the hydraulic oil is returned through the oil-hydraulic circuit from the hydraulic cylinder to the oil-hydraulic pump via a second port, a communication path, a minor gap between the movable valve and the valve seat, and a first port. In this process, the communication path allows for a smooth flow of the hydraulic oil from the second port into the movable valve.