To create a comfortable indoor environment by conditioning the air and distributing the air, by utilizing advantages that the earth temperature hardly changes and is stable throughout the year, it is warmer than the outside air in winter and is lower than the outside air in summer.

The in-ground heat is stored and retained by utilizing pumiceous porous small-stone like blocks (unglazed porcelain stone, pumice stone, porous hard resin and the like) at a lower section of a heat collecting pipe. The air kept warm in the ground is distributed to the lower section of the pipe by light wind from an upper fan, and the warm air is sucked from intermediate and upper sections to exchange heat, and distributed indoors through a dust removing filter and the like after air conditioned.