An operating member mounting structure includes a mounting plate having an inner edge defining a mounting hole, and an operating member includes a keytop and a flange which are coupled to each other by a shaft, and the flange is formed with a slit. The diameter of the flange is larger than that of the mounting hole. When the operating member is rotated and pressed down in a state that the slit receives the inner edge of the mounting hole, the flange passes over the inner edge of the mounting hole to be fully brought beneath the mounting plate. An operating shaft of an operated device is inserted into an insertion hole opened on the surface of the flange. By operating the keytop exposed from the top surface of the mounting plate, the operated device can be operated through the operating shaft.