An air conditioner comprising: a control device including: a plurality of indoor unit operation changers (110; 110-1, 110-2, 110-N) configured to be set to a cooling mode or a heating mode, and a plurality of indoor units (200; 200-1, 200-2, 200-N); an indoor unit out of the plurality of indoor units being connected to any one of the plurality of indoor unit operation changers and configured to perform a cooling operation or a heating operation according to a result of setting the plurality of indoor unit operation changers, wherein the control device is configured to, during an operation of the air conditioner: determine an operation mode of each of the plurality of indoor unit operation changers connected to respectively at least one indoor unit of the plurality of indoor units; detect an indoor unit operation changer at an operation mode corresponding to an operation mode of the said at least one indoor unit out of the plurality of indoor units, among the plurality of indoor unit operation changers; and determine which indoor unit operation changer is connected to the said at least one indoor unit out of the plurality of indoor units, among the plurality of indoor unit operation changers based on the result of detecting at least one of the indoor unit operation changers. a plurality of indoor unit operation changers (110; 110-1, 110-2, 110-N) configured to be set to a cooling mode or a heating mode, and a plurality of indoor units (200; 200-1, 200-2, 200-N); an indoor unit out of the plurality of indoor units being connected to any one of the plurality of indoor unit operation changers and configured to perform a cooling operation or a heating operation according to a result of setting the plurality of indoor unit operation changers, wherein the control device is configured to, during an operation of the air conditioner: determine an operation mode of each of the plurality of indoor unit operation changers connected to respectively at least one indoor unit of the plurality of indoor units; detect an indoor unit operation changer at an operation mode corresponding to an operation mode of the said at least one indoor unit out of the plurality of indoor units, among the plurality of indoor unit operation changers; and determine which indoor unit operation changer is connected to the said at least one indoor unit out of the plurality of indoor units, among the plurality of indoor unit operation changers based on the result of detecting at least one of the indoor unit operation changers. determine an operation mode of each of the plurality of indoor unit operation changers connected to respectively at least one indoor unit of the plurality of indoor units; detect an indoor unit operation changer at an operation mode corresponding to an operation mode of the said at least one indoor unit out of the plurality of indoor units, among the plurality of indoor unit operation changers; and determine which indoor unit operation changer is connected to the said at least one indoor unit out of the plurality of indoor units, among the plurality of indoor unit operation changers based on the result of detecting at least one of the indoor unit operation changers.