A first cap is mounted at a movable iron core, a second cap holding a valve member is fitted to the first cap, capable of displacement, an biasing force F1 of an iron-core return spring biasing the movable iron core toward an initial position and an biasing force F2 of a buffer spring interposed between the movable iron core and the valve member are set so as to have a relation of F1>F2, and when the movable core is located at the initial position, gaps x, y are interposed between the valve member and a regulating portion of the second cap and between an engagement projection portion of the second cap and a front end wall of an engagement recess portion of the first cap, respectively.