<p>An adhesive layer (27) is formed on the rear surface of a cover sheet (24). A dome-like contact spring (23) is bonded at the top portion thereof to the rear surface of the cover sheet (24) by the adhesive layer (27). A fixed contact (26a) and an annular contact section (26b) which can be switched to either an electrically conducted state or an insulated state by the contact spring (23) are provided on a printed circuit board (22). A light guide sheet (25) is provided on the front surface side of the cover sheet (24). In the front surface of the light guide sheet (25), there is formed an annular groove (28) (recess) not penetrating through to the rear surface side of the light guide sheet (25) and having a specific width, and the annular groove (28) is located at a position corresponding to the top portion of the contact spring (23).</p>
