To provide a heat exchanging system capable of realizing the operation of high efficiency of a heat pump by surely preventing the failure in collecting heat from the ground in summer, and effectively utilizing cold heat in accompany with collecting the heat.

This heat exchanging system comprises a storage tank 2 for hot water supply, a heat pump 1 for heating the water in the storage tank 2 for hot water supply, and an underground heat collecting means 3 buried in the ground. An underfloor heat collecting means 5 is mounted in an underfloor space of a building. The underground heat collecting means 3 and the underfloor heat collecting means 5 are switchably connected with the heat pump 1, and further connection switching means 21, 22 are mounted to switch and connect the underground heat collecting means 3 and the underfloor heat collecting means 5 with the heat pump 1. Further a temperature detecting means 25 for detecting a temperature of the underfloor heat collecting means 5 and a switch control means 24 for controlling the switching operation of the connection switching means 21, 22 are mounted. The switch control means 24 connects the heat pump 1 and the underground heat collecting means 3 by the connection switching means 21, 22 when a detected temperature of the temperature detecting means 25 is lower than a prescribed temperature.