In a fixing unit, a fixing roller is rotated under driving force transmitted from a paper discharge unit-side gear of a driving section via a fixing roller driving gear, and holds and conveys a recording medium in cooperation with a pressure roller in a nip region. When a control section determines that acceleration conditions are fulfilled, the driving section increases the rotating speed of the paper discharge unit-side gear so that it is rotated at higher speed than before-acceleration speed over predetermined high-speed rotating period.