A toner image fixing device realizes a stabilized fixing process by smoothly controlling a surface temperature of its heating roller (50), preventing peeling-off of a layer (52) of the roller core (51). The toner image fixing device comprises a heating roller (50) consisting of a core (51) covered with a layer (52) of, e.g., a silicon rubber, a heat lamp (53) mounted in the heating roller (50) and a pressure roller (60) for pressing a sheet of paper (40) against the heating roller (50). The toner image fixing device is provided with a temperature sensor (54) for sensing a surface temperature of the heat roller (50) and for operating the heater lamp (53) at a preset ON-OFF ratio (e.g., 1:3) to elevate the heating roller surface temperature from a first preset value to a second preset value and thereafter to maintain it at the second preset temperature.