PURPOSE: To heighten ceiling height, and to shorten the time for the execution of works by scaling down the space of the reverse side of a ceiling.

CONSTITUTION: A wooden verandah running on the two sides of a building is fixed at a corner section formed by the top face 1 and side face 2 of a building body, a wooden receiving member 4 is fastened at the proper position of the top face 1, and a holding member 7 with a receiving port 7A holding one side edge of a ceiling board 6 is installed to the side face of the wooden verandah running on the two sides of the building. A joiner 5 with a receiving port 5A holding one side edge of the ceiling board 6 is mounted on the underside of the receiving member 4. The ceiling board 6 held between the joiners 5 and the joiner 5 and the holding member 7 is formed of a light-weight foam having flame resistance.