To efficiently transmit and receive a large quantity of information, and to display operation information on each air conditioning unit without an unnatural feeling.

A front seat air conditioner ECU 46 imparts a transmission right of a multiplex communication line 58 to a front seat panel ECU 50, and acquires front seat switch information to generate front seat display information. The front seat air conditioner ECU 46 imparts a transmission right to back seat switch information in relation to a back seat panel ECU 54 while generating front seat display information. After imparting a transmission right to back seat sensor information in relation to a back seat air conditioner ECU 48, a transmission right is imparted to the front seat information in relation to the front seat air conditioner ECU 46, and the front seat display information is transmitted to the front seat panel ECU 50. The front seat panel ECU 50 is capable of displaying the latest front seat display information acquired on a display part 146 of the front seat panel 52 without delay.