Disclosed is an image forming system including an image forming device which includes a paper feeding tray, a print section which performs printing to papers fed from the paper feeding tray and a control section which controls so as to feed the printed papers to a post-processing device as a booklet main body to be book-bound, and the post-processing device which carries out ring-binding processing to the fed papers and book-binds a booklet, and the control section controls so as to feed a front cover paper, a back cover paper, papers for binding of the booklet to a ring-binding process section of the post-processing device along with the booklet main body, and a paper feeding order is in an order of the back cover paper, the papers for binding, the front cover paper and the booklet main body.