To prevent the discharge of drain by leading drain from an air conditioner to a buried drain pipe by an outdoor drain hose, and further leading the drain directly from a drain lead-in pipe, provided at the side part of a drain receiver of a drain, so as to be drained to a rain gutter.

A buried pipe 10 for inserting a rain gutter is disposed in a floor 7 piercingly in the direction of floor thickness from a drainage ditch 8, and a rain gutter 11 is connected to the lower part of the buried pipe 10. A drain 130 is disposed on the drainage ditch side of the buried pipe 10. An opening 131a is formed at the side part of a drain receiver 131 of the drain 130, and a drain lead-in pipe 14 is connected thereto. Drain from an air conditioner is led to a buried drain pipe 15 buried in the floor 7, by an outdoor drain hose, further led into the drain receiver directly from the drain lead-in pipe 14 and drained through the rain gutter 11. The drain from the air conditioner is not discharged to the floor and can be drained at a low cost without impairing a fine sight.