To reliably prevent a top plate from being removed without adding a release preventing component by providing restraining means preventing the movement of a coupling section in the releasing direction when a switch is fitted on the fitting section of a center pad.

An insertion hole 14 with a size for allowing movement of the fitting leg 6 of a base plate 5 is formed at the base face center of the recess (fitting section) 3 of a cover (center pad) 1, and release holes 15 with a size for allowing the transit of the tip of a T-shaped pin (coupling section) 12 are formed at three equal-angle positions. Lugs (restraining means) 16 having a shape excluding the narrow portion of a deformed hole (coupled section) 8 are formed at adjacent positions (adjacent positions in the releasing direction B) of the release holes 15 respectively. A through hole 17 passing the wirings of a fixed contact point 9 and a moving contact point 13 is formed on the back face of the recess 3. A horn switch 4 is fitted, the lugs 16 formed on the bottom of the recess 3 are inserted into the portions other than the T-shaped pin 12 of the deformed hole 8, and the movement of the T-shaped pin 12 in the releasing direction B is prevented.