A digital multi-function peripheral includes a multi-function peripheral unit that has plural functions, a switching power supply unit connected to a commercial power supply as a main power supply for the multi-function peripheral unit, and an electrical storage device charged in advance as an auxiliary power supply for the multi-function peripheral unit. The digital multi-function peripheral further includes a control circuit that monitors a load current flowing to the multi-function peripheral unit, supplies electric power from the electrical storage device to the multi-function peripheral unit instead of electric power from the switching power supply unit when the load current is smaller than a threshold set as an allowable lower limit of power efficiency of the switching power supply unit, and supplies the electric power from the switching power supply unit to the multi-function peripheral unit when the load current increases to be equal to or larger than the threshold.