PURPOSE: To save man-powers in the construction by forming a concrete form made of polyacetal resin, and making it possible to reuse it with its mechanical strength kept constant even if its material is recycled several times.

CONSTITUTION: In polyacetal resin constituting a concrete form, thermal plastic resin can be obtained by letting the class of aldehyde undergo addition polymerization by the action of carbonyl group. After the concrete form made of polyacetal resin has been used, it is heated and melted so as to be reused, and almost no reduction in strength is exhibited even if the form has been reused more than five times. Therefore, since it can be apparently recycled, cost can thereby be kept low with industrial waste reduced in quantity.