In an image reading system, a photographic film is conveyed, an image frame is conveyed to a reading position, pre-scanned and fine scanned. An image obtained by pre-scanning is displayed on a display section. The film is conveyed after the inspection processing ends. Further, by using data output from six image surface detecting sensors disposed along a transverse direction of the film, inter-frame region candidates (edge candidates) are detected within an inspection range per frame. A region surmised to be between frames is detected from film light amounts input from the sensors. Edge slopes, the edges' density differences, are computed as evaluation values for detecting an edge to be used as a reference from among the candidates, and are compared. An edge having a largest density difference is extracted. With the extracted edge as a reference, an image frame position is determined while considering an image frame size.