A fixing unit includes a fixing member, a pressing member, a heating device, a sheet width detector, and a heating area adjustor. The pressing member faces the fixing member to form a fixing nip between the fixing member. An un-fixed toner image is fixed on a recording medium when the recording medium passes through the fixing nip. The heating device heats the fixing member while maintaining a non-contact condition with the fixing member. The sheet width detector detects sheet width of the recording medium. The heating area adjustor changes a heating area of the fixing member, heatable by the heating device, based on the sheet width detected by the sheet width detector. The heating area adjustor is moveable in a space between the fixing member and the heating device along a sheet width direction to change a size of the heating area.