A printing section for performing duplex printing by performing printing on each printing paper sheet fed by a feeding section and performing printing on the other side of the one-side printed printing paper sheet that has been inverted by an inverting section; a control section for exert control to alternately perform the printing on each printing paper sheet from the feeding section and the printing on each one-side printed printing paper sheet; a post-processing time obtaining section for obtaining a post-processing time for each duplex printed printing paper sheet; and a feeding timing setting section for setting a feeding interval of the printing paper sheets from the feeding section based on the post-processing time for each duplex printed printing paper sheet, and calculating a paper spacing interval between each printing paper sheet from the feeding section and each one-side printed printing paper sheet based on the post-processing time.