PURPOSE: To make employment of floor panels in the same width possible by installing beams, intersecting partition walls of a collective housing, with the surfaces of the opposite beams being spanned with floor panels, and by fitting corner cutoffs of the floor panels to the corners of columns that support the beams at their ends.

CONSTITUTION: A plurality of dwelling spaces 2 are formed side by side in a collective housing with partition walls 1 provided between the spaces, and beams 3 are provided, intersecting the partition walls 1, in a plurality of rows. The opposite beams 3 are spanned with a plurality of floor panels 4. Of the floor panels 4, floor panels 4a that are installed at the end of the beams 3 are provided with cutoffs 6 at their corners and the cutoffs 6 are fitted to the corners of columns 5 that are supporting the beams 3 at their ends.