To provide a heat pump apparatus capable of starting defrosting operation at an optimal timing when efficiency becomes the best. (COP becomes a maximum value) A heat pump apparatus 100 includes a refrigerant circuit in which a compressor 1, a condenser 2, expansion means 3, and an evaporator 4 are serially connected. Condensation temperature detection means 11 that detects a saturation temperature of the condenser 2, and evaporation temperature detection means 12 that detects the saturation temperature of the evaporator 4 are provided. Operation efficiency is estimated by a value obtained by dividing heating ability estimated from a detection value of the condensation temperature detection means 11 by a difference between a detection value of condensation temperature detection means 11 and that of evaporation temperature detection means 12 or dissipation power estimated by the difference.
