Fixing device, image forming apparatus, and method for controlling fixing device, each of which is for setting temperature of fixing member and temperature of external heating section for heating fixing member in order to carry out fixing process with respect to recording material for which set fixing temperature needs to be set higher than warm-up completion temperature by predetermined temperature or more

摘要

In a case where a process is carried out with respect to an envelope in a fixing process mode, at least either (i) a set temperature of a fixing roller in a fixing process or (ii) a set temperature of an endless belt in the fixing process which endless belt is provided in an external heating device is changed in accordance with a time period between an end of a warm-up mode and a start of the fixing process mode. This makes it possible to prevent both a wrinkle and inadequate fixing in a fixing process of an envelope carried out by a fixing device of an external heating method.