To make the size during maintenance as small as possible and facilitate the assembly and the folding operations regardless of the sizes in right and left and the depth widths.

The frame holder is structured that between a pair of foot 13, a pair of upper/lower-cross pieces 14 are connected and the frame holder has the first framework 12 having supplementary poles 19 in the protrusive form that crosses continuously at a right angle with the cross-pieces 14, the second framework 20 linking a pair of upper/lower cross-pieces 22 between a pair of bents 21 and a pair of side poles 25 with their base ends attached to allow respective turn horizontally to the protruded ends of the supplementary poles 19. Further, while a groove like rail 27 is continuously formed along a lengthwise direction in the relatively facing inside of both side poles 25 and supplementary poles 19, at the edge of both ends of the second framework 20, a dowel that cannot be taken off and that can slide freely by being engaged within the rail 27, is installed, in which case, a plural number of casters 28 are installed at the bottom end and top and bottom boards are placed on both upper and lower parts. Thus, a housing framework is formed on the top end.