To improve working efficiency at a construction site by shortening a construction period.

This steel form structure 2 has a plurality of column forms 4, a plurality of main beam forms 6 and 8 having an upwardly opening groove, and a floor form 18 for covering a space S1 formed by being surrounded by the main beam forms 6 and 8 from above on the inside of the groove. The main beam forms 6 and 8 have respectively a bottom frame 22, side frames 24 and 26, a bottom frame 28 and a pair of side frames 30. The respective grooves are mutually communicated, and are arranged so as to communicate with the upper end of a cylindrical space in the respective column forms 4.