PURPOSE: To heat air heating a whole building and recovering the heat at the same time by means of thermal media to fulfill the heating of the whole building and obtain hot water or the like.

CONSTITUTION: The air heated by a heat-collector 42 installed on a roof of building is fed under the floor of building and the heated air is circulated from the space in the walls to the heat-collector 42. In this air circulation building, the heat-collector 42 forms heat-collecting spaces 45 partitioned by heat- insulating members at the rear side of roof plates 43 like iron plates constituting the roof. Glassplates 46 somewhat separated from the roof plates 43 are arranged at the front side of the roof plates 43 to form a closed space 49. And a heat-collective pipe 70 are arranged in the closed space 49 and the thermal media are circulated in the pipes 70 to collect the heat.