PURPOSE: To improve a coefficient of performance of a heat pump by a method wherein as refrigerant, mixed refrigerant of fuluorocarbon having a specified modulus of ozone decomposition and freezer machine oil is used and an absorption process device is assembled in a heat pump cycle.

CONSTITUTION: An evaporator constituting a part of a heat pump cycle is provided with a desorber 11 having a branch function and a resorber 13 in place of a condensor and there is provided an inner heat exchanger 16 for performing a heat exchanging operation between liquid of high concentration and liquid of low concentration. Mixed refrigerant comprising fluorocarbon with a modulus of ozone decomposition of 0.1 or less and freezer machine oil having action of absortion and condensing of refrigerant is stored in the desorber 11, fluorocarbon refrigerant evaporated through removal of heat from thermal medium fluid is compressed by a compressor 12 and sent to the resorber 13 under an over-heated vapor condition. In turn, the mixed liquid having increased concentration with the desorber 11 is sent to the resorber 13 by a liquid pump 15, where sensitive heat of the over-heated vapor is removed as condensation heat, thereafter the vapor is absorbed into the mixed medium and condensed there.