A supply oil passage is defined in a sleeve and communicates to a feed port to which oil is supplied. A valve object is able to be seated on or separated from a valve seat defined on an inner wall of the supply oil passage. A guide wall is defined by an inner wall of the sleeve, and the valve seat is located between the feed port and the guide wall. A forward flow port extends from the guide wall to an oil passage of an attachment component. A pressure chamber is defined in the sleeve, and the valve seat is located between the supply oil passage and the pressure chamber. A backflow port always allows the pressure chamber and the oil passage of the attachment component to communicate with each other. The forward flow port is located between the valve seat and the backflow port.