1. A method of detecting a frame edge of a film fed by first and second groups of light-receiving element arrays, said first group of light-receiving element arrays being composed of at least one array extending perpendicular to an advancing direction of said film, said second group of light-receiving element arrays being composed of at least one array extending in the same direction as that of said first group of light-receiving element arrays in such a manner as to be parallel with said first group of light-receiving element arrays, comprising the steps of: (a) preliminarily detecting the presence of said frame edge by said first group of light-receiving element arrays; and (b) precision-detecting the position of said frame edge by said second group of light-receiving element arrays after preliminary detection of said frame edge.