To provide a structure constructing method for constructing a ceiling slab and a floor slab, and repeatedly reusing a form used for construction without applying a cross-sectional chipped part to a ceiling joist and a floor joist.

A length adjustable flat surface molding form material is prepared by the required number. After adjusting this material in the length so that the tip of the respective flat surface molding form materials does not protrude in a molding material filling space of a joist molding form between opposed upper edge and upper edge of the two joist molding forms separated in the horizontal direction, a molding material pouring floor surface is constructed by adjacently extending by the required number. A molding material is poured in the required thickness as a slab into this molding material pouring floor surface. The joist molding form is disassembled by waiting for solidifying this molding material, and respective flat surface molding forms are separated and recovered from a mold.