To provide a good seal maintainability and good coupling between members of a case at a low cost by introducing a case member to be coupled, say cover and frame in a press and pressing them at specified pressure and temp. for specified time.

A PCMCIA case 1 has a top and bottom faces composed of separate covers 2, side ends formed with a frame 3 and a left narrow side face formed with a socket connector piece 4. At specified position R in the region of the frame 3 of the case 1, it is pressed at a pressure of 0.5-2N/mm2 and temp. of 120-180° for about 5-10sec during adhering, then cooled and released from the press. This attains a seal maintainability at a high level.