To prevent a plate spring for obtaining the operational feeling of an opening and closing cover from falling off of the fitting portion even if an electrical component receives a large impact.

A protrusion 23 is formed on an eccentric portion of a rocking medial axis 21 of an opening and closing cover 20 fit to a front panel 10. A plate spring 30 in elastic contact with the protrusion 23 is inserted in and fitted to an opening 13 of a front panel 10 side. A presser strip portion 60 for preventing the escape of a fitting portion 31 of the plate spring 30 from the opening 13 is formed integrally with a frame 35 of a push button unit 40 fixed to the front panel 10 by use of resin. A presser strip portion 61 is placed against a wiring board 50.