An image forming apparatus includes an image forming unit, a fixing unit having a heating member for generating heat based on power supplied, a detection unit, and a controller. The image forming unit forms an image on a sheet. The fixing unit fixes the image on the sheet by the heat of the heating member. The detection unit detects a temperature of the heating member. The controller controls power to be supplied to the heating member based on a temperature detected by the detection unit. The controller determines a difference value between the temperature detected by the detection unit and a target temperature, determines an accumulated value by performing accumulation processing of the difference value, and controls the power based on the difference value and the accumulated value. The controller controls the accumulation processing based on the difference value and the accumulated value.