To facilitate an erection work by constituting a concrete form with posts whose height can be adjusted, girders which is provided with insertion recesses and fixed to the posts, pipes inserted in the recesses, and synthetic resin boards mounted on the pipes.

Post 1 are vertically extended or contracted by rotating a handle 2 and girders 3 are laid on the upper end of the posts 1. Pipes 6 are inserted in recesses 4 of support boards 5 of the girders 3 and transparent or translucent synthetic resin boards 7 are laid on the upper face of the pipes 6. Then, after reinforcements or the like have been laid on the synthetic resin boards 7, concrete is placed on the boards 7 to form a floor face. In this way, since pipes 6 are supported in the recesses 4 on assembling the form and the intervals are not shifted, the interval can be shortened and hence, small diameter pipes can be used as the pipes 6. Accordingly, the weight of pipes 6 per unit area can be reduced and hence, transportation, assembling, and disassembling can be facilitated.