A refrigerant piping from a compressor is connected to an indoor heat exchanger via a four-way valve. The refrigerant piping from the indoor heat exchanger extends via an electronic expansion valve and then branches in two directions and one is connected to an oil refrigerant heater via a two-way valve and the other to an outdoor heat exchanger via a two-way valve. The refrigerant piping from the oil refrigerant heater is connected to the compressor, while the refrigerant piping from the outdoor heat exchanger returns to the compressor via the four-way vale and a check valve. An operation control part conducts a control of switching over a heat pump operation and a refrigerant heating operation, according to an outdoor air temperature signal from an outdoor air temperature sensor. |