An air conditioning device which includes: a refrigerant circuit including an outdoor unit and indoor units connected to each other via an interconnecting pipe (71,72); and an operation controller controlling operation of the refrigerant circuit, the interconnecting pipe (71,72) including: a liquid main pipe connected to the outdoor unit, and liquid branch pipes branching off from the liquid main pipe and each connected to a corresponding one of the indoor units; and a gas main pipe connected to the outdoor unit, and gas branch pipes branching off from the gas main pipe and each connected to a corresponding one of the indoor units, and the controller including an air-conditioning capacity controller (37a, 47a, 47b) determining a target value of an evaporation temperature or a condensing temperature of the refrigerant circuit, depending on air-conditioning load in a room, and, based on the target value, controlling operational capacity of the compressor in the refrigerant circuit, wherein the operation controller includes an oil collection controller calculating an amount of refrigerating machine oil accumulated in the interconnecting pipe (71,72) during the operation, and when the calculated amount exceeds a preset amount, performing oil collecting operation for collecting the refrigerating machine oil in the refrigerant circuit into the compressor, and characterised in that the oil collection controller includes an oil accumulation amount calculator that compares (i) a current value of the target evaporation temperature or the target condensing temperature of the refrigerant circuit with (ii) a set value of the evaporation temperature or the condensing temperature of each of the indoor units, wherein the set value is a reference value corresponding to the lower limit flow rate of a gas refrigerant necessary for the refrigerating machine oil to flow with the refrigerant without accumulating in the gas branch pipe; and when the gas branch pipes are determined to include a gas branch pipe which does not satisfy the lower limit flow rate, the oil accumulation amount calculator determines that the refrigerating machine oil is accumulating in the gas branch pipe and calculates an amount of the refrigerating machine oil accumulated in the gas branch pipe. a refrigerant circuit including an outdoor unit and indoor units connected to each other via an interconnecting pipe (71,72); and an operation controller controlling operation of the refrigerant circuit, the interconnecting pipe (71,72) including: a liquid main pipe connected to the outdoor unit, and liquid branch pipes branching off from the liquid main pipe and each connected to a corresponding one of the indoor units; and a gas main pipe connected to the outdoor unit, and gas branch pipes branching off from the gas main pipe and each connected to a corresponding one of the indoor units, and the controller including an air-conditioning capacity controller (37a, 47a, 47b) determining a target value of an evaporation temperature or a condensing temperature of the refrigerant circuit, depending on air-conditioning load in a room, and, based on the target value, controlling operational capacity of the compressor in the refrigerant circuit, wherein the operation controller includes an oil collection controller calculating an amount of refrigerating machine oil accumulated in the interconnecting pipe (71,72) during the operation, and when the calculated amount exceeds a preset amount, performing oil collecting operation for collecting the refrigerating machine oil in the refrigerant circuit into the compressor, and characterised in that the oil collection controller includes an oil accumulation amount calculator that compares (i) a current value of the target evaporation temperature or the target condensing temperature of the refrigerant circuit with (ii) a set value of the evaporation temperature or the condensing temperature of each of the indoor units, wherein the set value is a reference value corresponding to the lower limit flow rate of a gas refrigerant necessary for the refrigerating machine oil to flow with the refrigerant without accumulating in the gas branch pipe; and when the gas branch pipes are determined to include a gas branch pipe which does not satisfy the lower limit flow rate, the oil accumulation amount calculator determines that the refrigerating machine oil is accumulating in the gas branch pipe and calculates an amount of the refrigerating machine oil accumulated in the gas branch pipe.