Patent ID: 8000616

Claim:
An image forming system comprising: an image forming unit configured to form an image; a paper output option unit configured to output a sheet on which an image is formed by the image forming unit; a detecting unit configured to detect the size of a sheet in a direction in which the sheet is conveyed to the image forming unit; a controller configured to specify a paper output port of the paper output option unit to output a sheet of a preset size; and wherein the controller determines whether there is a paper output port of the paper output option unit capable of outputting a sheet of a size larger than the preset size in order to continue the image forming operation, in response to sheet size mismatch information indicating that the size of the sheet detected by the detecting unit is larger than the preset size, before the detection of the size of the transfer medium is completed, and changes the specification from the specified paper output port to the paper output port capable of outputting a sheet of the size larger than the preset size.