A movable board with movable contact points is arranged inside a switch case formed by overlap of a substrate with fixed contact points and a lid body. A top end surface of the substrate has a concave streak portion and a ring groove for accommodating a seal ring, wherein a projecting streak portion provided on a lower surface of a flange portion in the lid body is fitted in the concave streak portion for welding. A seal bearing mounted to shaft holes provided on an opposing portion between the substrate and the lid body comprises a cylindrical body portion fitted in at least one of the shaft holes, and a lip-shaped seal portion extending to a side of a rotary surface of a shaft portion from an inner peripheral surface of the body portion to make flexible contact with the rotary surface.