A movable contact point board provided with contact points is urged in a direction of being away from stationary contact points by return springs each having the same size and the same characteristic, and is arranged as opposed to the stationary contact points. Return springs have the respective ends for supporting locations in the movable contact point board which are away from each other as having the contact points in the movable contact point board therebetween and support heights of the return springs at the stationary side differ with each other by D. When a plunger equipped with a holding portion having a flat surface as a bottom surface presses the movable contact point board, the contact point in the movable contact point board gets in contact with the stationary contact point at an inclined posture. Thereafter, while the movable contact point board becomes perpendicular to the axial direction, a contacting point between the contact point in the movable contact point board and the stationary contact point varies to perform the wiping function.