To reduce the cost by commonalizing a pair of right and left engaging members and, at the same time, simplifying a structure of an interior finish member supporting body.

A pair of engaging members 22 are formed in the same shape includes a holding section 22a for holding a steel framed beam 2a, a supporting section 22 connecting the interior finish member supporting body 23 and a connecting section 22c for connecting the holding section and the supporting section. The interior finish member supporting body 23 is formed of the same sectional shape extended in the longitudinal direction. The holding section 22a is conveyed to a site in an imperfect state to open an upper plate, and it is bent according to the thickness (t) of the steel framed beam to complete the U-shaped holding section.