PURPOSE: To change not only width but also shape by rigid-body-combining plural rectangular parallelopiped modules freely attachably/detachably in a horizontal direction.

CONSTITUTION: A top board construction 20 is constituted by rigid-body- combining freely attachably/detachably at least two rectangular parallelopiped modules M equipped with the rigidity not to deform and destruct in a vertical direction and a horizontal direction. The rectangular parallelopiped modules M are hollow boxes and constituted of square upper and lower plates 22 and both side plates 24. In this case, a background plate 26 may be provided on a rear surface and at least a front surface is released. Namely, the outside edge surface of a side plate 24 facing the rectangular parallelopiped modules M is protruded in the horizontal direction and the rigid body combination is executed. Thus, not only the width but also the shape can be changed.