To provide an air conditioner which can reduce power consumption as much as possible when the pressure and flow rate are adjusted at a transportation circuit on a secondary side.

A refrigeration circuit 12 on a primary side supplies a first refrigerant compressed to be a high temperature and a high pressure by a compressor 14 to a first heat exchanger 18 or a second heat exchanger 21 between the compressor 14 and an expansion valve 19. A transportation circuit 13 on a secondary side circulates a second refrigerant, which exchanges thermal energy with the first refrigerant by means of the second heat exchanger 21, between the second heat exchanger 21 and a third heat exchanger 27. The pressure in the transportation circuit 13 is adjusted at a refrigerant tank 28. At adjustment of pressure, the thermal energy of the first refrigerant is used.