A printer comprising: an image former that forms a plurality of images on a plurality of sheets; a circulation transfer route composed of a first transfer route that transfers each sheet fed from a feeding route toward a discharging route, and a second transfer route that is branched from the first transfer route and returns each sheet received from the first transfer route to the first transfer route; a printing rate detector that detects a printing rate of each image; a circulation number determiner that determines a circulation number of each sheet on the circulation transfer route based on the printing rate of each image; a scheduling coordinator that coordinates a sheet transfer schedule based on the circulation number of each sheet; and a transfer drive controller that controls quantities described in the sheet transfer schedule by controlling driving mechanisms on the circulation transfer route and switching between the first and second transfer routes based on the schedule.