In a vehicle air-conditioning system, an evaporator is disposed in an air-conditioning case to form a bypass passage through which air bypasses the evaporator, and an opening degree of the bypass passage is adjusted by a bypass door. When a vehicle engine operates, the system performs a cold-storing mode where cold quantity stored in condensed water on the evaporator is increased. On the other hand, when operation of the vehicle engine is stopped, the system performs a cold-releasing mode where air passing through the evaporator is cooled by cold released from frozen condensed water. During the cold-storing mode and the cold-releasing mode, temperature of air blown into a passenger compartment can be adjusted by adjusting the opening degree of the bypass passage. Thus, in the vehicle air-conditioning system, cold-storing quantity in the evaporator can be improved while power-saving effect of the vehicle engine is improved.