To make electrically conductive a coupling section to reduce leak of electromagnetic wave from a casing by placing independent conductive member in contact with an internal surface of each member at the coupling sections of a plurality of insulating members.

A casing for a portable telephone set is formed by coupling a right wall body 3 and a left wall body to a box type wall body 2 having no wall body in the right and left side. Here, the internal surface of the wall body 2 and right wall body 3 is coated with conductive films 41, 42 in the thickness of about 20 to 100μm. These conductive films 41, 42 are placed in contact with each other at the area in the width of 3mm to 10mm where the wall body 2 and right wall body 3 are coupled. The wall body 2 and left body are also coupled in the same manner as explained above. Thereby, since the wall body 2 and right wall body 3, wall body 2 and the left wall body are respectively placed in conductive electrically at the coupling area, the electromagnetic wave is reflected and absorbed thereby reducing remarkably the leak of electromagnetic wave from the coupling area.