AIR-CONDITIONER

PROBLEM TO BE SOLVED: To improve energy efficiency in an air-conditioner with a refrigerant circuit. SOLUTION: A compressor 32, an outdoor heat exchanger 37, an indoor heat exchanger 34, and the like are connected by a refrigerant piping 31 to form a refrigerant circuit 30 of a closed circuit. A four-way switching valve 33 is provided at the refrigerant circuit 30 to invert the circulation direction of a refrigerant. A refrigerant heater 42 is provided at the refrigerant circuit 30. In cooling operation, a solenoid valve 41 is closed and the outdoor heat exchanger 37 becomes a condenser to perform refrigeration cycle operation. In heating operation, a natural gas is burnt by the refrigerant heater 42, and a refrigerant is heated by a high-temperature combustion gas for evaporation. The evaporation refrigerant flows into an indoor heat exchanger and exchanges heat with indoor air for condensation, and thus the indoor air is heated.