A frame image (210) with 5-mm wide margins is formed on a paper sheet on the basis of the leading end and widthwise end positions of the paper sheet (107) detected by a contact image sensor (CIS) (204) in an adjustment mode. After that, this paper sheet (107) is circulated to a feed position via a circulating path (206) and paper convey path (205), and the CIS (204) detects the frame image position formed on the circulated paper sheet and its paper end portion so as to detect errors from the 5-mm wide margins. Correction values which can cancel these errors are stored in a correction parameter storage unit (71), and forming start timing control is made using these correction values upon forming an image in an actual job. In this way, an image forming apparatus which can detect the paper feed timing with high precision, can eliminate deterioration of the image position precision due to mounting errors and durability of components, and can always precisely adjust the image position is provided.