The invention provides a manual operation button having a large operable area. A manual operation button is composed of a manual operation plane, a holder for assembling the manual operation plane and a stopper for fixing the holder to a casing. The casing has a mounting hole having substantially the same size and shape as the manual operation plane, so that when the manual operation plane is assembled to the mounting hole, the manual operation plane forms a substantially continuous flat plane with the casing. The holder includes a substantially L-shaped mounting portion for mounting to the casing, a flat plate-like mounting plane for mounting the manual operation plane, and a hinge portion connecting the mounting portion and the mounting plane. The whole width of the hinge portion is disposed within the outer projection plane of the manual operation plane.