A valve element in a valve chamber is movable between an OFF position and an ON position to switch a flow quantity of fluid between a large flow quantity and a small flow quantity. The valve chamber has a fluid passage including an outer passage defined between an inner periphery of the valve chamber and an outer periphery of the valve element. The valve chamber has a throttle shape to decrease in inner diameter gradually from upstream toward downstream to decrease a minimum passage area of the fluid passage in a non-linear form. The valve chamber increases a differential pressure across the valve element in a linear form relative to a stroke of the valve element when the valve element moves from the OFF position toward the ON position.