An image forming apparatus which includes a reading unit and allows an external memory device to be attached the apparatus, displays, on a display unit, a screen for performing a function using the reading unit and the external memory device when the image forming apparatus returns to the active state from the power-saving state depending on a cause for returning, if the cause for returning is that an original document is placed on the reading unit, and the external memory device is attached. The image forming apparatus also displays a default screen on the display unit when the image forming apparatus returns to the active state from the power-saving state, if the cause for returning is that an original document is placed on the reading unit, and the external memory device is not attached.