1. An air-conditioning apparatus in which a refrigerant circuit is formed by connecting, by a refrigerant pipe, a compressor that discharges a refrigerant, which is a zeotropic refrigerant mixture including a plurality of components with different boiling points, an outdoor-side heat exchanger that exchanges heat between air outside an air-conditioning target space and the refrigerant, a first expansion device that regulates a pressure of the refrigerant, and a load-side heat exchanger that exchanges heat between air in the air-conditioning target space and the refrigerant, the air-conditioning apparatus comprising a controller, the controller including: a composition computing function unit configured to compute a circulating composition, the circulating composition representing a value of composition of each of components in the refrigerant circulating through the refrigerant circuit; and a composition determining function unit configured to determine whether or not a computation result of the composition computing function unit is correct, adopt a value of the composition of each of the components, the value being set in advance and related to composition as the circulating composition if the computation result is determined as incorrect, and adopt the computation result as the circulating composition if the computation result is determined as correct.