An image forming apparatus is provided. The image forming apparatus includes a fixing unit to thermally fix an image transferred onto a sheet thereto, an endless belt to carry the sheet in a feeding path toward the fixing unit, a pattern forming unit to form an image pattern on the belt, a sensor to detect presence of the sheet being carried by the belt, and a judging unit to judge as to whether the sheet is in one-sided alignment, in which the sheet is aligned to one of the widthwise sides in the feeding path based on a result detected by the sensor.