Abstract: In a heat pump system according to the present invention, at least part of a plurality of outdoor heat-exchanging flow paths that pass through an outdoor heat exchanger is alternately selected as a flow path for defrosting and is used, and the other flow path is used as a flow path for evaporation so that defrosting and a heating operation can be simultaneously performed. In addition, the refrigerant in which a defrosting action is performed, while passing through the outdoor heat exchanger, is throttled and then is used for an evaporation action so that the structure of the heat pump system is simple and both heating and defrosting can be performed.