A vehicular air conditioning system comprising: a refrigerating cycle circuit, the refrigerating cycle circuit comprising a compressor for compressing a cooling medium for air conditioning, an outside heat exchanger for heat exchange between the cooling medium for air conditioning and outside air, and an inside air conditioning heat exchanger for heat exchange with air to be blown off to the interior of a vehicle room, the compressor, the outside heat exchanger and the inside air conditioning heat exchanger being annularly connected in order; and a device cooling circuit, the device cooling circuit comprising a heating unit, an inside cooling heat exchanger for heat exchange with air to be blown off to the interior of the vehicle room, an intermediate heat exchanger for heat exchange between a device cooling medium for cooling the heating unit and the cooling medium for air conditioning present in the refrigerating cycle circuit, and a pump for circulating the device cooling medium, the heating unit, the inside cooling heat exchanger, the intermediate heat exchanger, and the pump being annularly connected, the intermediate heat exchanger being constructed such that one end of a piping of the cooling medium for air conditioning is connected to a liquid piping, the liquid piping providing connection between the outside heat exchanger and the inside air conditioning heat exchanger, and an opposite end of the piping of the cooling medium for air conditioning is connected to a suction port of the compressor, characterized in that the outside heat exchanger is connected to a suction port or a discharge port of the compressor in a switchable manner by first flow path switching means, and the inside air conditioning heat exchanger is connected to the suction port or the discharge port of the compressor in a switchable manner by second flow path switching means, and the intermediate heat exchanger is connected to the suction port or the discharge port of the compressor in a switchable manner by the first flow path switching means. a refrigerating cycle circuit, the refrigerating cycle circuit comprising a compressor for compressing a cooling medium for air conditioning, an outside heat exchanger for heat exchange between the cooling medium for air conditioning and outside air, and an inside air conditioning heat exchanger for heat exchange with air to be blown off to the interior of a vehicle room, the compressor, the outside heat exchanger and the inside air conditioning heat exchanger being annularly connected in order; and a device cooling circuit, the device cooling circuit comprising a heating unit, an inside cooling heat exchanger for heat exchange with air to be blown off to the interior of the vehicle room, an intermediate heat exchanger for heat exchange between a device cooling medium for cooling the heating unit and the cooling medium for air conditioning present in the refrigerating cycle circuit, and a pump for circulating the device cooling medium, the heating unit, the inside cooling heat exchanger, the intermediate heat exchanger, and the pump being annularly connected, the intermediate heat exchanger being constructed such that one end of a piping of the cooling medium for air conditioning is connected to a liquid piping, the liquid piping providing connection between the outside heat exchanger and the inside air conditioning heat exchanger, and an opposite end of the piping of the cooling medium for air conditioning is connected to a suction port of the compressor, characterized in that the outside heat exchanger is connected to a suction port or a discharge port of the compressor in a switchable manner by first flow path switching means, and the inside air conditioning heat exchanger is connected to the suction port or the discharge port of the compressor in a switchable manner by second flow path switching means, and the intermediate heat exchanger is connected to the suction port or the discharge port of the compressor in a switchable manner by the first flow path switching means.