An automotive dual air-conditioning system having No. 1 air conditioner and No. 2 air conditioner arranged separately in an automobile, for controlling air-conditioning operation, and a bus line connected between No. 1 air conditioner and No. 2 air conditioner. No. 1 air conditioner transfers air-conditioner control information to No. 2 air conditioner through the bus line during operation of No. 1 air conditioner and No. 2 air conditioner, to thereby control the operating condition of No. 2 air conditioner in accordance with the information thus supplied. Furthermore, No. 2 air conditioner changes the control of its operating condition to manual control in case a communication error of air-conditioner control information to be transferred through the bus line continues over a specific period of time.