PURPOSE: To improve an outer appearance of an outer wall of a building, cooling capability and to prohibit frosting from adhering to the outer wall.

CONSTITUTION: A duct A and a duct B are installed at a side part of an outdoor unit. A double-staged compressor 22, a four-way valve 24, an outdoor heat exchanger 21, a bypassing unit 30, a main pressure reducing device 26 and an indoor heat exchanger 20 are cooperatively arranged in sequence. The bypassing unit 30 is comprised of a bypassing pressure reducing device 31, a gas-liquid separator 32 and check valves 35 to 38. The bypassing unit 30 is connected to a liquid bypassing pipe merging part 40 of the double-staged compressor 22. A discharging side 41 of a low pressure side compressing mechanism of the double-staged compressor 22 and a suction part 28 of a high pressure side compressing mechanism are connected to the liquid bypassing pipe merging part 40, thereby an outer appearance of a building is improved, its cooling capability is also improved and a frosting on the building can also be prevented.