Abstract: A method for forming a duplex print, in which a recording sheet has images formed on both sides thereof, includes steps of: setting an interleave number depending on a size of the recording sheet; forming the duplex prints under a condition where the number of the recording sheets located in a transport path is equal to or less than the interleave number; determining whether or not a size of the recording sheet supplied from a paper supplying unit is changed; changing the interleave number to a minimum interleave number when the size of the recording sheet is changed; forming the duplex prints with respect to the new sized recording sheet under a condition where the number of the recording sheet located in the transport path is equal to or less than the minimum interleave number. The present invention also provides an apparatus for forming a duplex print, which operates in accordance with the method for forming a duplex print.

Abstract: A method of forming a two-sided print in an image forming apparatus comprises the steps of forming images on first sides of L recording sheets, leaving M recording sheets having images printed on the first sides thereof in the transport path with a non-stacked arrangement, where M.gtoreq.2, and sequentially forming images on the first sides of N-L recording sheets and forming images on second sides of N recording sheets in a predetermined sequence dependent on values of L, M and N.