An image forming apparatus includes an image forming unit; a fixing device; a main power circuit configured to supply electric power; an auxiliary power circuit configured to store and supply the electric power; a switching device configured to switch between a charge and discharge mode for the auxiliary power circuit; and a control device configured to, when the image is formed by a facsimile function, control the switching device so as to operate the auxiliary power circuit not in the discharge mode so that the electric power of the main power circuit is supplied to the fixing device, and when the image is formed on the basis of other functions, control the switching device so as to operate the auxiliary power circuit in the discharge mode so electric power of the main power circuit and that of the auxiliary power circuit are supplied to the fixing device.