PURPOSE: To prevent the duplicate starting of respective air condition devices from happening regardless of the operation mode for a plurality of air condition ing devices which jointly use a power source with a limited capacity.

CONSTITUTION: A time differential value of a common bus bar current IL which is detected by a current detector 6 is operated by a differential operator 11, and the current differential value is larger than a specified value or not is compared by a comparator 12, and when it is larger than the specified value, a signal SC1 is output. Then, an interlocking circuit 5A is constituted in such a manner that a signal SL1 is output by a timer 13 after an estimated period of time which is considered to be required for the start transient condition of the air conditioning device to be damped sufficiently has passed from the time when the signal SC1 is received, and the start commands to respective air conditioning devices are locked so that any of other air conditioning devices may not be started during the continuation of the signal SL1.