Abstract: An apparatus measures a dynamic power consumption in each of component devices at a time intervals and subtracts the sum of the dynamic power consumptions from a predetermined maximum value to obtain a dynamic margin. When a request for connecting an emergency device to a power supply is issued, the apparatus compares the rated power consumption in the emergency device with the dynamic margin. If the rated power consumption in the emergency device exceeds the dynamic margin, the apparatus selects, as a disconnectable device, a component device having an individual margin calculated by subtracting the dynamic power consumption from the rated power consumption is greater than an excess of power amount over the dynamic margin of the rated power consumption in the emergency device and the lowest priority.