An image forming apparatus capable of returning from the power saving state and performing user authentication by one action of holding an authentication card over a card reader even when the apparatus is in the power saving state. The apparatus performs short-distance wireless communication with an external device. A controller performs control processing including at least authentication processing. When short-distance wireless communication with the device is started, a short-distance wireless communication section delivers a return-starting interrupt, to the controller, receives authentication data from the device to thereby store the authentication data during returning of the apparatus. The controller performs authentication processing based on the stored authentication data after returning of the apparatus from the power saving state, and notifies the device of an authentication processing result by a different channel.