Picture images being joined without connection gaps can be produced with high quality by adjusting a position error, even if an error is included in a scanning position being detected, and by preventing a map missing area from arising which is caused by the adjustment of position error. A position error detection circuit detects a position error from picture information consisting of image data inside a scanning area being read overlapped by a line image sensor and storage data being stored in an image memory. Next, the position error detection circuit adjusts a scanning position coordinate for cancelling this position error, which is then output to a mapping circuit as an adjustment position coordinate. The mapping circuit stores the image data to the image memory according to the adjustment position coordinate.