To achieve stable operation of a heat-pump heating and cooling system using geothermal heat, without collecting geothermal heat in excess, thereby reducing the consumption of geothermal energy, and preventing freezing of areas around a location where geothermal heat is collected.

A water heat exchanger 10 for collecting geothermal heat and an air heat exchanger 11 for ventilation are connected in series over a heat-pump refrigerant cycle in order to stably operate a heat pump without collecting the heat source of the heat pump in excess from under the ground, so as to fully secure the heat-exchange area and the heat source of the system.