To make it difficult for dusts to enter an operation part, and decrease conduction defects between a fixed contact and a movable contact.

On the upper face of a plate board 3 on which first and second fixed contacts 8, 9 are installed, a dome-like operation part 4 is arranged which is elastically deformable and has a first and a second movable contacts 10, 11, then on the lower face of this operation part 4 a mounting pin part 13 is installed which is press fitted into a through-hole 12 of the plate board 3, and on the outer periphery of this mounting pin part and on the lower face of the operation part 4, an air vent groove 14 is installed that continues from the inner part of the operation part 4 via the mounting pin part 13 to the lower face side of the plate board 3. Consequently, by press fitting the mounting pin part 13 into the through-hole 12 of the plate board 3, the inner part of the operation part 4 and the lower face side of the plate board 3 are communicated by the air vent groove 14, and the air can be circulated. By this, the elastic deformation of the operation part 4 can be made easier, and since the lower face of the plate board is made difficult to be adhered with the dusts, the inner part of the operation part 4 becomes hard for the dusts to enter, thus the conduction defects of each contact can be reduced.