A shaft outputs a thrust force in an axial direction by using a magnetic flux caused by an electric current flowing through a coil. A housing is made of resin and retains the shaft. The housing has a base portion having an outer circumferential surface, which is configured to be entirely in contact tightly with a sealing member. The housing further has a distal portion having an outer circumferential surface defining a depression. The outer circumferential surfaces of the base portion and the distal portion are substantially equal in diameter and are formed continuously.