A fixing device including a fixing belt module is formed of a fixing roller having a heat source, one or more tension rollers at a fixing side and an endless fixing belt looped and stretched around the rollers to thereby rotate and a pressure belt module including an endless pressure belt that comes in contact with an outer peripheral surface of the fixing belt only within a range of a section where the fixing belt is wrapped around a surface of the fixing roller, thereby forming a nip section for fixation between itself and the fixing belt. The fixing belt module includes a fixing belt heating unit that heats an inner peripheral surface and/or the outer peripheral surface of the fixing belt at any sections other than the section where the fixing belt is wrapped around the outer peripheral surface of the fixing roller.