Abstract: In an apparatus for detecting a pattern of crest lines according to the present invention, an object area to be treated is mechanically divided into a plurality of picture elements (Ej), and the direction of crest lines such as a dactylogram can be easily detected by a simple calculation consisting of addition, subtraction, multiplication, and division, by using evaluated shading values in a series (Si) of picture elements, each unit area (UA) consisting of some picture elements of all picture elements in the object area. Therefore, even when the crest lines are cut off, crushed, or branched off, on the way thereof, the direction of the crest lines can be correctly detected.