In a construction wherein at the start of fixing, a pressure belt is brought into contact with a fixing roller at uniform timing, it has sometimes been the case that the temperature of the pressure belt at a point of time whereat the fixing is started does not become a desired temperature but faulty fixing occurs. The timing for bringing the pressure belt into contact with the fixing roller at the start of fixing is changed in accordance with the detected temperature of the pressure belt. By such a construction, faulty fixing can be prevented from occurring.