The present invention provides the actuator, which is capable of preventing biased abrasion by lowering a surface pressure at a contact portion of a movable element with a guide surface and increasing a movable range, in which a specified output force can be gained. Magnetic resistance of at least one of the surfaces (Y1, Y2) of first and second yoke parts (5, 6) corresponding to peripheral surfaces (P1, P2) of a plunger (7), on which magnetic flux acting surfaces are formed by energization, is unbalanced in the circumferential direction so as to act a resultant force of magnetic forces acting on the movable element in the radial direction eccentrically to a radial one end (E1) side.