PURPOSE: To utilize part of or all of the collected solar heat for microorganic fermentation so as to utilize the resultant heat for heating a desired object.

CONSTITUTION: A heat transmission pipe 3' transmits the heat accumulated in a heat accumulator 5 to a silo 6. The heat transmission pipe 3' is partly laid under the compost 7 buried underground in a greenhouse. Inside the silo 6, the entire part of the stored compost 7 is uniformly heated by the heat transmission pipe 3' laid in its interior. The resultant heat fermentation heat is directly released to the inside of the greenhouse 1, or it can be gradually released when necessary after the recovered heat is temporarily accumulated in the heat accumulator 5 by using the heat transmission pipe 3' laid inside the silo 6 in a reverse manner or by attaching a heat transmission pipe 3' for recovering the heat to the silo 6.