A fixing device of an embodiment is configured to fix an unfixed toner image formed of a decolorable toner on a sheet of paper. The fixing device includes: a fixing unit including a fixing member heated by a first heat source and a pressure member heated by a second heat source; a first temperature sensor and a second temperature sensor; and a temperature controller configured to control the first heat source and the second heat source separately for temperature control based on detected temperature information acquired by the temperature sensors, wherein the temperature controller controls the surface temperatures of the fixing member and the pressure member to set equal or above the temperature at which fixing is started fixing starting temperature and to set below the temperature at which decolorization is started, and such that the surface temperatures of the fixing member and the pressure member become substantially the same temperature.