PURPOSE: To improve the high lift of an air-conditioning apparatus while prolonging the life of a refrigerant pump by driving an auxiliary pump unit until a difference pressure is made lower than a predetermined value when the difference pressure at an outlet and an inlet of the refrigerant pump exceeds another predetermined value.

CONSTITUTION: An air-conditioning apparatus is constructed with refrigerant cycles on heat source and utilization sides. An auxiliary pump unit is constructed with a second four-way valve 22, a second refrigerant amount adjusting tank, and a second refrigerant pump 23, and being of the utilization side refrigerant cycle, and is disposed between an indoor machine and an outdoor machine. Further, sensors 18, 19 detect inlet pressure and outlet pressure in a first refrigerant pump of the utilization refrigerant cycle. In a control device 26, estimation means 29 estimates a difference pressure between the inlet pressure and the outlet pressure detected by detector means 27, 28, and means 30 drives the auxiliary pump units 22, 23 in response to the difference pressure. The driving is performed from the time the difference pressure exceeds a first predetermined value to the time the difference pressure becomes lower than a second predetermined value.