To obtain an excellent feeling of operation by preventing an operation button part from tilting when operated by depression without making an apparatus large-sized, and to suppress noises due to vibration of the operation button part when the depressing operation is removed.

An operation button member 5 attached to an exterior cover 4b of an apparatus body includes an operation button part 13, an attachment part 10 fitted to an internal surface of the exterior cover 4b, a support arm 11 which connects the attachment part 10 and the operation button part 13 to each other and elastically supports the operation button part 13, and elastic arms 14a, 14b which are extended from the support arm 11 in a direction along an inner surface of a back cover 4b. The elastic arms 14a, 14b elastically deform with the operation button member 5 attached to the exterior cover 4b to generate energizing force, and while extension-directional tip parts 15a, 15b of the elastic arms 14a, 14b are pressed against an inner surface of the exterior cover 4b with the energizing force, a press shaft 12 of the operation button part 13 is pressed against a switch held on an apparatus body.