An image forming apparatus that can detect a leading edge of a tabbed sheet after skew correction with high accuracy and without increasing a size of the apparatus. A transfer unit transfers a toner image to the sheet, the skew of which having been corrected based on a detection result of a first skew detection unit, while the toner image is controlled to be synchronized with the sheet based on the detection result of the first skew detection unit and a detection result of a second skew detection unit.