According to one embodiment, a fixing device includes a belt, a heater, and a holder. The belt is formed into a cylindrical shape, is rotated in a circumferential direction to transport a sheet, and applies heat to the sheet. The heater is arranged on an inner side of the belt and extends in a predetermined longitudinal direction to heat the belt. The holder extends in the longitudinal direction of the heater and holds the heater. The holder includes a support portion and a retraction portion. The support portion comes into contact with the heater and supports the heater. The retraction portion is provided at a position avoiding the support portion in the longitudinal direction of the heater, and includes a smaller contact area with the heater than the contact area between the support portion and the heater or does not come into contact with the heater.