An air-conditioning system that performs a refrigeration cycle in a refrigerant circuit, includes: an outdoor unit; a plurality of indoor units; and a connection pipe disposed between the outdoor unit and the indoor units and that forms at least a refrigerant passage through which refrigerant in a gas-liquid two-phase state flows. The connection pipe includes: a branch portion that includes an indoor-side pipe group including indoor-side pipes that each communicates with any one of the indoor units, and diverges refrigerant flowing from the outdoor unit side; and a trap portion disposed in at least any one of the indoor-side pipes and is filled with refrigerant in a gas state.