PURPOSE: To minimize the flow path resistance of the cooling air and to improve the cooling efficiency by using (n) pieces of housings to form a housing unit with a specific arrangement of those housings where the cooling air exhausting faces are set in a single direction.

CONSTITUTION: As shown in the figure, eight pieces, for example, of housings 30 of the same structure are arranged to form a housing unit. These housings 30 are set in a cross form to enclose exhaust spaces 31. The right side of an intake face 34 is defined as a maintenance face 33, and the air exhausted to the space 31 is led toward the ceiling. Thus the cooling air 32 passes through a slit 39 of the face 34 and is exhausted into the space 31 via a printed base board 38 and a fan case 36. The air 32 passed through an electronic device 37 is exhausted toward the ceiling from the space 31. Each housing 30 contains a door 40 on the face 33 to attain the easy maintenance.