A fixing device in an image forming apparatus includes a rotatable fixing member; a plurality of heat sources to heat each area of the fixing member in a longitudinal direction thereof; a pressure member configured to contact the fixing member and forming a nip in association with the fixing member; a nip forming member disposed inside the fixing member and opposite the pressure member to form a fixing nip; a temperature controller to detect temperature at each area of the fixing member and control the temperature via lighting control performed by the heat sources; and a plurality of temperature sensors to detect temperature of the fixing member or the pressure member in each heating area heated by the plurality of heat sources. When a sheet size set by the image forming apparatus and an actually conveyed sheet size are different, operating speed of the device is adjusted.