A vehicle air-conditioning system includes: an HVAC unit that blows air whose temperature has been adjusted by a refrigerant evaporator and a second refrigerant condenser; a heat pump cycle in which a refrigerant compressor, a refrigerant circuit changeover section, a first refrigerant condenser, a first expansion valve, and the refrigerant evaporator are sequentially connected, in which a second expansion valve and a refrigerant / coolant heat exchanger are connected in parallel with the first expansion valve and the refrigerant evaporator, and in which the second refrigerant condenser is connected in parallel with the first refrigerant condenser; and a coolant cycle in which a coolant circulating pump, a ventilation-exhaust-heat recovery unit, a motor / battery, an electric heater, and the refrigerant / coolant heat exchanger are sequentially connected, and in which the ventilation-exhaust-heat recovery unit, the motor / battery, and the electric heater can be selectively used as a heat source.