To transfort a two-story building at a time by one truck by putting the first floor part into the second floor part of a unit house.

Wall boards 22a-22d for a second floor part and a roof 25 are provided in the second floor part 20. Floor boards 11 for the first floor, wall boards 12a, 12b, 12c, 12d for the first floor which are almost similar to the wall boards for the second floor and one size smaller and slidably inserted inward, and floor-cum-ceiling boards that the second floor boards 21 and the first floor ceiling 15 are vertically constituted as a unit. Fixing means 18, 19 fixing the first floor part 10 and the second floor part 20 in the state that the second floor part 20 is positioned in a specified location on the second floor boards 21 are provided in the structure. The first floor columns 13a-13d are used for guide rails and casters are fitted to the inside of the second floor part corresponding thereto.