To provide a method by which the upper half of an enclosure divided into upper and lower halves can be aligned easily with side enclosures on both sides and the enclosure can be installed in a short time even when no sufficient space is available above the upper half and a mechanism used for the method.

Guide members 6 and 6 and suspending members 4 and 4 are detachably attached in advance to both side enclosures 5 and 5 and the upper half 2 of an enclosure 1, respectively. The suspending members 4 and 4 are put on the guide members 6 and 6 and, at the same time, the upper half 2 is suspended between the enclosures 5 and 5 by lifting up the upper half 2 put in front of the lower half 3 of the enclosure 1 and moving the upper half 2 to the back sides of the enclosures 5 and 5. Then, after the half 2 is slid while the projecting sections 41 and 41 of the suspending members 4 and 4 are guided by means of the guide members 6 and 6 until the sections 41 and 41 come into contact with check plates 63 and 63 by applying a force to the upper half 2 from the front side, the upper half 2 is fixed to both side enclosures 5 and 5 with connecting bolts 14, 14,... passed through the first through holes 11, 11,... and the second through holes 12, 12,... of the box bodies 5 and 5 corresponding to the first holes 11, 11,... of the upper half 2.