Patent ID: 8301073

Claim:
An image forming apparatus, provided with a post-process apparatus for performing a post-process on recording paper output from the image forming apparatus, the image forming apparatus and the post-process apparatus constituting an image forming system, the image forming apparatus comprising: an image forming section capable of two-side printing for forming images on both sides of the recording paper and one-side printing for forming an image on one side of the recording paper; and a recording paper carrying section comprising an inversion carrying route and an output roller, the recording paper carrying section for, in the two-side printing, outputting the recording paper from the output roller to the post-process apparatus without switching back the recording paper by the inversion carrying route, and for, in the one side-printing, switching back the recording paper by the inversion carrying route and thereafter outputting the recording paper from the output roller to the post-process apparatus, the recording paper carrying section controlled by a controller such that a velocity of the recording paper output from the output roller for the one-side printing is higher than that for the two-side printing, the post-process apparatus comprising a carrying roller and a central processing unit, the post-process apparatus configured to temporarily stop the carrying roller of the post-process apparatus when changing a recording paper carrying velocity in the post-process apparatus in accordance with an instruction received at the central processing unit from the controller of the image forming apparatus related to a change in the velocity of the recording paper output from the output roller of the recording paper carrying section, the paper output velocity being a velocity at which the recording paper is sent from the image forming apparatus to the post-process apparatus, and thereafter increase the carrying velocity to a predetermined velocity stored in a memory which is in accordance with the paper output velocity, the image forming apparatus further comprising: printing process generation detection means for detecting generation of one of the one-side printing and the two-side printing within a predetermined period stored in a memory while the post-process apparatus causes the carrying roller to continuously rotate and then stops the rotation after performing the other of the one-side printing and the two-side printing; and first change-of-paper-output-velocity prevention means for controlling the recording paper carrying section or both of the recording paper carrying section and the image forming section so that the paper output velocity does not change, when the printing process generation detection means detects generation of said one of the one-side printing and the two-side printing.