Image forming apparatus and image forming system

An image forming system including:

• an image forming apparatus provided with (i) a paper feeding section in which a sheet of paper is stored, (ii) an image forming section for performing image formation on a sheet of paper, (iii) an output section for outputting, from the apparatus, a sheet of paper subjected to image formation, (iv) a main conveying path extending from the paper feeding section to the output section via the image forming section, and (v) a sub-conveying path through which a sheet of paper having one side finished with image formation is guided to an upstream side of the image forming section from an upstream side of the output section in the main conveying path;
• and a post-processing apparatus for performing a post-process on a sheet of paper outputted from the output section, the image forming system comprising:
• conditional judgment means for judging whether or not conditions for image formation are as follows:
• (1) double-side image formation is performed, i.e., images are formed on both sides of a sheet of paper;
• (2) the number of sheets of paper that constitute a single set is an odd number;
• (3) the number of sets is not less than two;
• and (4) it is necessary to delay image formation of the next set in order to perform a post-process on the previous set outputted ahead;
• and
• sequence control means for, when the conditional judgment means judges that double-side image formation is performed, that the number of sheets of paper of a single set is an odd number, that the number of sets is not less than two, and that it is necessary to delay image formation of the next set, changing (i) timing of feeding and conveyance of sheets of paper and (ii) an order in which images are formed in performing double-side image formation on plural sets of sheets of paper in succession, so as to make it possible to perform image formation on the next set while performing a post-process on the previous set.