PURPOSE: To provide the mounting method of the earphone cap in such a way that the earphone cap is not protruded from a case, then the earphone cap is caught by something resulting in being damaged at carrying or in operation, not standing in the way of other operation function components, the mount space is decreased and the miniaturization is attained.

CONSTITUTION: A rib 17 provided to a rear side of the earphone cap 20 is brought in contact with an inner wall 14a of a projection 14 of a case 10 at a rising part of the earphone cap 20 so that the earphone cap 20 cannot be opened by 90° or over to prevent the earphone cap 20 from being protruded from the case 10, a defect of the earphone cap 20 caught by something resulting in being damaged at carrying or in operation is avoided, and the earphone cap 20 is not standing in the way of other operation function components, the mounting space is reduced and the miniaturization is attained.