An image forming apparatus is provided with a fixing unit in which flickers can be effectively reduced while inhibiting electric current imbalance. The fixing unit comprises a fixing heater, a switching unit for switching the fixing heater on/off with an AC power source, and a control unit which controls the switching unit to switch in units of the half wave period of the AC power source AC, and a storing unit for storing a plurality of energization patterns which define the ways of performing the switch control. Each energization pattern corresponds to a control cycle which contains a three or more odd number of the half wave periods each of which is either an OFF period and an ON period, and all the half wave periods of the smaller in number of the ON periods and the OFF periods are not successively arranged.