In order to provide an authentication system and a terminal capable of saving user's trouble and allowing quick and accurate determination as to whether the user is a registered user or not, a data processing device capable of data communication with a plurality of image forming apparatuses decides an IC card standard used by an IC card reader connected to each image forming apparatus, and transmits a signal notifying the standard to the image forming apparatus having a corresponding identification ID. Based on the IC card standard decided by the data processing device, the image forming apparatus sets the IC card standard used by the IC card reader and determines whether or not the user is a registered user.