To reduce site works and to improve the safety of works by installing a form body arranged around a beam steel frame and frames disposed along the longitudinal direction of the form body at regular intervals.

An approximately U-shaped sectional form body 1 crossed at right angles in the longitudinal direction is arranged around a beam steel frame 3 constituting an SRC beam, and frames 2 are disposed along the longitudinal direction of the form body 1 at regular intervals. The upper end sections of the frames 2 are constituted so as to be joined with the end section of a cotter member 7 arranged so as to pierce the frames 2, between a beam steel frame 3 and a beam reinforcement 8 configuring the SRC beam together with the beam steel frame and concrete. The form body 1 is supported by the beam steel frame 3 by connecting the upper end sections of the frames 2 to the end section of the cotter member 7. Accordingly, site works can be reduced while the safety of works can be improved when the SRC beam is built.