PURPOSE: To prevent the rocking of a shutter to close a unit housing space and facilitate the inspection and service of the shutter mechanism, with respect to a unit array device wherein a plurality of units are housed and arranged in a plug-in manner.

CONSTITUTION: A hinge section 3 is formed at the upper part of the housing area opening 6 in a chassis 2 to be an outlet/inlet to a housing space, and a lock section 4 containing a permanent magnet 5 is formed at the lower part. A shutter 7 is anchored to the hinge section 3 on its upper end. When the shutter 7 is put in a perpendicular position due to gravity, its magnetic lock area 13 close to the lower end of the shutter 7 is brought into contact with the permanent magnet 5 in the lock section 4 and secured there by magnetic force. The shutter 7 is large enough to be secured in such a manner and close the housing area opening 6.