A method for sorting slide films stored in a magazine. One slide film has a mount made of a rigid material such as thick paper, and an exposed film or a picture image is mounted on the mount. In a sequence of operations to take out a film slide from a magazine storing a plurality of slides, transport the same for a predetermined treatment and transport again to another place for storing the same in a different magazine or a bucket, a dummy slide which can be easily discerned is inserted for every group of slides sorted according to an arbitrary classification, for example by clients or by subjects, to thereby facilitate a sorting operation.