In the present invention, when a first protrusion of a shaft abuts on a guide face thereby pressing a first valve element toward the top as seen in the drawing, the guide face is separated from a cylinder seat face, and a large-diameter oil passage is opened. At this time, when the first protrusion abuts on the guide face thereby driving the first valve element to the position where the valve opens, the first valve element is also pressed in a direction perpendicular to the reciprocating direction of the first valve element because the guide face has a spherical surface or a tapered surface. Thus, the first valve element is supported at two points, point E and point F or G, thereby dampening vibrations.