PURPOSE: To prevent a voltage drop in a power supply system caused by a concurrent energization at the time of recovery from service interruption in the case where many air conditioners are connected to the same power supply system.

CONSTITUTION: An electrical energization timing for a reset signal to be supplied to a micro-processor is optionally set by a time setting circuit. Switches 99 to 101 for optionally setting a time up to a starting of operation of each of air conditioners after resetting signals are provided and then a controlling operation for changing a time up to the operation starting is carried out by a micro-processor in response to a setting of each of the switches. With such an arrangement, it is possible to prevent any concurrent energization of each of the air conditioners at the time of recovery from service interruption and further to prevent any voltage drop in the power unit.