A refrigerant charging method for an air-conditioning apparatus (100, 200, 100A), wherein the air-conditioning apparatus (100, 200, 100A) includes a first refrigeration cycle, in which a first compressor, a heat-source-side heat exchanger, a first expansion device (16a to 16c), a first intermediate heat exchanger (15a, 15b), and a first passage of a heat exchanger for heating are connected through a first refrigerant pipe, a use-side heat exchanger (26a to 26d) connected through a first heat medium pipe to the first intermediate heat exchanger (15a, 15b), wherein a first heat medium flows through the first heat medium pipe, and a second refrigeration cycle, in which a second compressor, a second passage of the heat exchanger for heating, a second expansion device, and a second intermediate heat exchanger are connected through a second refrigerant pipe, a hot-water storage tank connected through a second heat medium pipe to the second intermediate heat exchanger, wherein a second heat medium flows through the second heat medium pipe, wherein heat of the first refrigerant and heat of the second refrigerant are exchanged by the heat exchanger for heating, the first intermediate heat exchanger (15a, 15b) exchanges heat between the first refrigerant and the first heat medium, and the second intermediate heat exchanger exchanges heat between the second refrigerant and the second heat medium, and wherein the heat exchanger for heating is connected to the first refrigerant pipe and the second refrigerant pipe so that the first refrigerant which is supplied to the first passage of the heat exchanger for heating and the second refrigerant which is supplied to the second passage form counterflow, characterized in that a first refrigerant which is charged to the first refrigeration cycle and a second refrigerant which is charged to the second refrigeration cycle are each a zeotropic refrigerant mixture having different saturated gas temperatures and saturated liquid temperatures under a same pressure, the refrigerant charging method comprising: when a first temperature difference is a difference between a saturated gas temperature of the first refrigerant at an inlet side and a saturated liquid temperature of the first refrigerant at an outlet side in the heat exchanger for heating, and when a second temperature difference is a difference between a saturated gas temperature of the second refrigerant at an outlet side and a temperature of the second refrigerant at an inlet side in the heat exchanger for heating, holding a difference between the first temperature difference and the second temperature difference in a predetermined value of 1 degree C or less by charging the second refrigerant to the second refrigeration cycle so that a plurality of single refrigerants forming the second refrigerant have a predetermined mixing ratio. a first refrigeration cycle, in which a first compressor, a heat-source-side heat exchanger, a first expansion device (16a to 16c), a first intermediate heat exchanger (15a, 15b), and a first passage of a heat exchanger for heating are connected through a first refrigerant pipe, a use-side heat exchanger (26a to 26d) connected through a first heat medium pipe to the first intermediate heat exchanger (15a, 15b), wherein a first heat medium flows through the first heat medium pipe, and a second refrigeration cycle, in which a second compressor, a second passage of the heat exchanger for heating, a second expansion device, and a second intermediate heat exchanger are connected through a second refrigerant pipe, a hot-water storage tank connected through a second heat medium pipe to the second intermediate heat exchanger, wherein a second heat medium flows through the second heat medium pipe,