PURPOSE: To simply fix a form, and concurrently assure its strength and accuracy.

CONSTITUTION: The three dimensional curved surface form is made up of a plurality of horizontal comb plates H1 through H11, and of vertical side plates V1 and V2 assembled with the side surfaces of the comb plates. First, the lowermost and the uppermost horizontal comb plate H1 and H2 are formed into polygons ABC and DEF on the form fixing side V with their effective width W assured, next, it is affirmed whether or not there exist any swelled section 11 where the form curved surface sides S of the horizontal comb plates H1 through H11 are swelled to the form fixing side V in the vertical cross section of a form unit 10, and when the effective width W is insufficient, either one or both of the apexes E and B of the polygons are moved to the form fixing side V, and the effective width W is assured in the respective vertical cross sections. Next, the apexes A and D, B and E and C and F of the corresponding polygons ABC and DEF are connected to each other respectively, and each vertically connected line segment AD, BE and CF is equally divided into a plurality of stages, and each line connecting equally divided points at each equal level shall be the cutting plane line of the horizontal comb plates H1 through H11 at the form fixing side V.