Provided is a heat-pump-type vehicle air conditioning system that passes hot gas to both a vehicle-cabin-exterior condenser and a vehicle-cabin-exterior vaporizer during a defrosting operation, and that, even during times of low outside air temperature, can efficiently defrost in a short period of time and can use the cooling cycle of an existing system as-is. In the heat-pump-type vehicle air conditioning system (1): a vehicle-cabin-interior condenser (8) disposed downstream of a vehicle-cabin-interior vaporizer (7) within an HVAC unit (2) is connected, with refrigerant switching means (16) therebetween, to a cycle (23) for cooling comprising an electric compressor (15), a vehicle-cabin-exterior condenser (17), a first decompression unit (19) with on-off valve function, the vehicle-cabin-interior vaporizer (7), and an accumulator (21); a vehicle-cabin-exterior vaporizer (27) disposed at the outside of the vehicle cabin is connected, with a second decompression unit (26) with on-off valve function therebetween, to the exit-side liquid refrigerant pipe (22B) of the vehicle-cabin-exterior condenser (17); and furthermore a bypass circuit (32) having a third decompression unit (30) with on-off function is connected between the accumulator (21) and the exit exit-side liquid refrigerant pipe (22B) of the vehicle-cabin-exterior condenser (17).