An air-conditioning apparatus in which at least one load side unit including a load side heat exchanger is connected to a heat source side unit including a compressor , a heat source side heat exchanger , and an expansion device , and a refrigerant is circulated between the units to form a refrigeration cycle, the apparatus comprising: a measurement unit that measures an operating state quantity of the refrigeration cycle of the air-conditioning apparatus; and a control unit including time constant calculation means that estimates a response time constant at a time when an opening degree of the expansion device is changed on the basis of specifications of the compressor that forms the refrigeration cycle, specifications of a condenser heat exchanger, and the operating state quantity of the refrigeration cycle, control constant calculation means that calculates at least either of a control gain of the opening degree of the expansion device , and a control interval on the basis of a calculation result of the time constant calculation means and a measurement result of the measurement unit, control constant change means that changes the control gain or the control interval on the basis of the calculation result of the control constant calculation means , and expansion device control means that changes the opening degree of the expansion device on the basis of the control constant, when the response time constant is estimated in the time constant calculation means , information regarding an operating frequency of the compressor , and information regarding at least any of an internal capacity of the heat source side heat exchanger , an internal capacity of the load side heat exchanger , and a displacement of the compressor are used, and the state quantity of the refrigeration cycle is degree of superheat of the refrigerant to be sucked into the compressor, a refrigerant temperature at the discharge side of the compressor, or degree of supercooling at the outlet of the outdoor heat exchanger. a measurement unit that measures an operating state quantity of the refrigeration cycle of the air-conditioning apparatus; and a control unit including time constant calculation means that estimates a response time constant at a time when an opening degree of the expansion device is changed on the basis of specifications of the compressor that forms the refrigeration cycle, specifications of a condenser heat exchanger, and the operating state quantity of the refrigeration cycle, control constant calculation means that calculates at least either of a control gain of the opening degree of the expansion device , and a control interval on the basis of a calculation result of the time constant calculation means and a measurement result of the measurement unit, control constant change means that changes the control gain or the control interval on the basis of the calculation result of the control constant calculation means , and expansion device control means that changes the opening degree of the expansion device on the basis of the control constant, when the response time constant is estimated in the time constant calculation means , information regarding an operating frequency of the compressor , and information regarding at least any of an internal capacity of the heat source side heat exchanger , an internal capacity of the load side heat exchanger , and a displacement of the compressor are used, and the state quantity of the refrigeration cycle is degree of superheat of the refrigerant to be sucked into the compressor, a refrigerant temperature at the discharge side of the compressor, or degree of supercooling at the outlet of the outdoor heat exchanger. <EOS>