An image forming apparatus comprising a fixation device having a heating part for heating and fixing a toner image formed on a recording medium is provided, which comprises a rotational velocity detecting part for detecting a rotational velocity of a conveyance roller for conveying the recording medium and a control part for estimating a surface temperature of the recording medium based on the rotational velocity of the conveyance roller detected by the rotational velocity detecting part, for estimating a temperature change of the heating part at a time of fixation based on the estimated surface temperature, and for determining a heating control variable of the heating part based on the temperature change.