1. A system for recognition of a shape pattern, which comprises a. causing a pattern input device to read the projection on a reference line of the shape pattern of an article subjected to pattern recognition and set in position at a given postural angle with reference to said reference line, b. converting the resultant output from the pattern input device into corresponding projection values, c. subjecting said projection values to differentiation twice in two stages of differential circuits, d. continuing the whole procedure described in steps (a), (b) and (c) until the rotation thereof covers one complete circle, e. detecting the fact that each side of the polygon of the shape pattern has fallen exactly into the direction of projection in accordance with the change in the initial value of the output from said differential circuits, f. putting to memory the rotary postural angle of the shape pattern and the projection value existing at the time of said detection and g. accomplishing the recognition of shape pattern on the basis of the rotated postural angle and the projection value obtained as described above.