Provided is an image forming device including: a sheet number control part for controlling a maximum processable sheet number set on a paper attribute basis for a finisher for finishing a printed sheet; an automatic tray switching part for switching an initially selected tray part to another tray part when paper runs out in the midst of print processing on sheets fed from the initially selected tray part to continue the print processing, the initially selected tray part being initially selected from a plurality of tray parts holding sheets of different paper attributes; and a tray switch determining part for, when a feeding tray part runs out of paper in the midst of print processing set to execute finishing, determining whether to actuate the automatic tray switching part on the basis ofmaximum processable sheet numbers and a paper attribute of paper of a selectable tray part candidate.