1. An edge detecting apparatus, comprising: i) filtering means for performing filtering processing with a difference filter and on two pixels in an image, which pixels are adjacent to each other, and thereby obtaining a difference between pixel values of the two pixels, which are adjacent to each other, and ii) judgment means for making a judgment as to whether an absolute value of the thus obtained difference is or is not equal to at least a predetermined threshold value, the judgment means judging that, in cases where the absolute value of the difference has been judged to be equal to at least the predetermined threshold value, an edge is located between the two pixels, which are adjacent to each other.