PURPOSE: To reproduce a state where the fixing position of a frame is adjusted by providing an engaging part on the bottom of a box and a part for securing a coupling member to a frame and then engaging the frame with the box under a state where the fixing part of the frame is inserted into the through holes of the frame and the coupling member.

CONSTITUTION: A box 1 comprises a box body 11, frame fixing metals 12, bolts 13, and nuts 14. The frame fixing metals 12 are provided at four corners on the bottom of the box 1 and the bolts 13 are planted thereat. Frames 2, 2 for fixing a board 7 are provided, at the upper and lower parts thereof, with through holes 2a being inserted idly with the bolts 13. The frame 2 is coupled through a pair of vertical couplers 3 having longitudinally and laterally elongated holes 3a, 3b at the opposite ends thereof. The board 7 fixed with a plurality of units 8 through screws 6 is secured, on time opposite sides of bent parts 71, 72, to the frames 2, 2 on the opposite sides through screws. This structure realizes easy and positive positioning of each part.