To detect a groove portion present in a film splice definitely distinctively from a film impression and the like and reliably irrespective of the width and depth thereof.

For detecting a splice between one film and another extending in a film width direction, while the film 1 is longitudinally unrolled and run, three positions in the film width direction detect a recessed portion 2 in the film 1, and the output of detection signals from all the positions leads to detection of the splice.