PURPOSE: To allow a water with melted snow from the floor of am inner balcony, of a building constructed in a cryogenic place, to flow down in good performance without re-freezing.

CONSTITUTION: A drain gutter 50 is provided in such a way as lead from the floor 12 of an inner balcony 10 to an indoor place through one side wall 16b, and further to the below outside through the indoor place, and is thereby precluded from freezing certainly to exert a good function as a drainage path. An accommodation chamber 200 is provided adjacent to the side wall 16b of this inner balcony 10, and a draining gutter 50 is arranged in this accommodation chamber 200 so as to prevent drop of the intra-room design value and achieve effective utilization of the space.