Patent ID: 8190049

Claim:
An image forming apparatus, comprising: (A) a sheet feeding section in which a sheet is stored; (B) an image forming section for forming an image on the sheet; (C) a first discharging section for discharging, to outside the apparatus, the sheet on which the image is formed; (D) a main carrying path for directing the sheet from the sheet feeding section to the first discharging section through the image forming section; (E) a first sub-carrying path for directing the sheet on which one side an image is formed, from an upstream side of the first discharging section in the main carrying path to an upstream side of the image forming section; and (F) a second sub-carrying path for directing the sheet from the upstream side of the first discharging section in the main carrying path to a second discharging section, said image forming apparatus and a post-processing device constituting an image forming system, the post-processing device being attachable to the image forming apparatus and performing a post-process with respect to a sheet discharged from the first discharging section, said image forming apparatus, further comprising: (G) a wait-time occurrence judgment section for judging whether or not it is necessary to delay an image formation to be processed for a second image forming job so that time required to perform a post-process for a first image forming job followed by the second image forming job is secured; (H) a single-side image formation judgment section for judging whether or not the second image forming job is for a single-side image formation in which an image is formed only on one side of a sheet; and (I) a stacked sheet discharge control section for controlling, when the wait-time occurrence judgment section judges it to be necessary to delay the image formation and the single-side image formation judgment section judges the second image forming job to be for the single-side image formation, a sheet carrying mechanism in the main carrying path, the first sub-carrying path, and the second sub-carrying path so that (i) a first sheet for the second image forming job which first sheet is fed to the first discharging section through the main carrying path is carried in a switchback manner to be directed from the first discharging section to one of the first and second sub-carrying paths so as to be in a stand-by state, (ii) a second sheet for the second image forming job which second sheet is fed to the first discharging section through the main carrying path is carried in a switchback manner to be directed from the first discharging section to the other of the first and second sub-carrying paths so as to be in a stand-by state, and (iii) the first sheet and the second sheet which are in the stand-by state are again carried in a switchback manner so that the first sheet, the second sheet and a third sheet for the second image forming job which third sheet is fed to the first discharging section through the main carrying path and is not in a stand-by state are concurrently and overlappingly discharged.