PURPOSE: To set a pair of facing woods for forming a V-shaped groove accurately and straightly in the thickness direction of a PC plate when the V-shaped groove becoming the folding part of a folding-type PC form is formed.

CONSTITUTION: A reinforcing member 24 positioned at an intermediate layer is set in a form 18 for preparing a PC form. The reinforcing member 24 is formed of a steel sheet and it is stretched in the left and right direction to open extendedly a slit formed in the first region 32. A plurality of V-shaped cuttings are formed alternatively left and right at the central part of the second region corresponding to the folding part of the PC form. These cittings are successively folded upward and downward to form a plurality of cut and raised pieces 40. Facing woods 26 and 28 are held by the cut and raised piece 40 of the reinforcing member 24 set on the form 18 and under this condition, concrete is cast in the form 18.