To add a required filling amount of refrigerating machine oil into a refrigerating cycle from an oil tank provided in an outdoor unit when installing an air conditioner so that a refrigerating machine oil amount corresponds to the dimension of the length of piping connecting the outdoor unit with an indoor unit.

The air conditioner includes: the indoor unit including a heat exchanger 6 and an expansion valve 5; the outdoor unit including a compressor 1, a four-way valve 2, a heat exchanger and an expansion valve; a control device 18 controlling the respective component elements installed in the outdoor unit; and field piping 7 connecting the outdoor unit with the indoor unit and forming a refrigerant path. In the outdoor unit, from a high pressure side to a low pressure side of the compressor 1, there are arranged the oil tank 8 storing the refrigerating machine oil, solenoid valves 9, 10 provided on both sides of the oil tank and a capillary 12 provided on a solenoid valve side of the low pressure side. The control device 18 controls an opening time of the solenoid valves 9, 10 for additionally filling an amount of the refrigerating machine oil corresponding to the length of the field piping 7 into the refrigerating cycle from the oil tank.