To perform indoor air conditioning by natural convection of the air in a living space by combining a plurality of heat exchangers and utilizing a temperature of the groundwater.

In this system, the heat exchangers 5, 6, 7 for performing the heat exchange between the water as a heat medium and the air circulated in an air circulating passage are mounted on underfloor spaces S1, S2 of living spaces R1, R2 and an under-roof space S3, the air after heat exchange is allowed to flow out from the air circulating passages of the heat exchangers 5, 6, 7 to be convected in the living spaces R1, R2, heat medium circulating passages of the heat exchangers 5, 6, 7 are formed as a closed circulating passage 300, and a ground water circulating passage 400 for circulating the groundwater exchanging the heat with ground heat is used as a heat source-side passage of a heat pump H applying the closed circulating passage 300 as a load-side passage.