A fixing unit for printers or copiers includes a heater, in the fixing unit, for heating a fixing member to fix a toner image on a sheet; a zero-cross detector for detecting zero-cross timings of electric power when a voltage of the electric power is at zero volts; a switching circuit for turning on and off the electric power to the heater; a controller for controlling the switching operation of the circuit so as to provide a first state in which the electric power is continuously supplied to the heater for a second state in which the electric power is not supplied to the heater for a multiple of half-cycles from one of the zero cross timings. In the fixing unit, the electric power is supplied to the heater with an intermittent pattern, including the second state, for a predetermined period after at least one of a turn-on operation of the heater and a turn-off operation of the heater.