A fixing device includes a sensor driving unit that drives a temperature sensor to be movable in an axial direction of a fixing rotating body, and a sensor position control unit that controls the position of the temperature sensor by the sensor driving unit. The sensor position control unit performs sensor position control for setting a sheet size identified by a size identification unit as a reference sheet size and allowing the temperature sensor to be located within a passage area of a sheet having the reference sheet size and a non-passage area of a sheet having a sheet size smaller by one size than the reference sheet size.