To reduce the number of stops of a compressor provided at a heat pump apparatus in a heat pump system using a heating appliance by a natural convection system.

A control apparatus 100 sets a supply temperature by which a COP that has been stored previously becomes a predetermined value with respect to an outdoor temperature as a restrictive temperature. The control apparatus 100 controls an operating frequency of a compressor 1 between a lower limit frequency and an upper limit frequency which have been set previously so that the supply temperature should become a target temperature which has been set previously, and when the supply temperature becomes the preset restrictive temperature, the control apparatus 100 temporarily stops the compressor 1.