PURPOSE: To emit a radio wave to an external space stably when the radio equipment is inserted to a personal computer or the like and the personal computer is in use.

CONSTITUTION: The small sized radio equipment which has a nearly flat rectangular case 1 having a radio circuit in the inside and in which an antenna 2 is mounted to an outer surface, and which is inserted to an opening of other device 7 and in use has a case extension section 4 consisting of a conductor made cylinder enclosing part of the case 1 and fitted thereto and of a conductor made flange 4' coupled with one end of the cylinder and having a window to expose the antenna. The flange 4' closes electrically a gap between the case 1 and an opening of the other device 7 to which the small sized radio equipment is inserted.