An image forming apparatus which is capable of achieving both enhanced userfriendliness and improved energy saving efficiency without being released from a reduced power consumption state by a user who has no will to use the same passing thereby. When a copying machine 200 is in a sleep mode, it is detected whether or not a user has come near to the copying machine 200. If a contactless IC 600 is present within the range of radio wave signals emitted from an IC tag reader/writer 500, it is determined that a user has come near because the communication between the contactless IC 600 and the IC tag reader/write 500 can be carried out. Reading of data from the contactless IC 600 is started, and user authentication is executed based on the data. If, as a result of the user authentication, the user is a licensed user, it is determined whether or not an original document has been set on an automatic feeder 800. When an original document has been set on the automatic feeder 800, the copying machine 200 is caused to return to a normal mode as a normal power consumption state from the sleep mode.