PURPOSE: To improve maintainability of stairs by a method wherein the upper end of a through-column to support stairs and the upper end of the wall panel of an upper story part are intercoupled by using a connection beam.

CONSTITUTION: An upper story extended along an outer wall and having an outer edge supported by a floor beam and stairs arranged outside the upper story floor in parallel to the upper story floor and intercoupling the lower story and the upper story floor are built to an outer wall W of a plurality of storied housing body the housing outer wall of which is built by using a wall panel P. Further, a through-column 4 extending to the upper story and supporting the stairs is located at the floor beam and besides the upper end of the through-column 4 and the upper end of a wall panel P of an upper story part are intercoupled through a connection beam 5.