a device for measuring the contour length of a two - dimensional pattern comprises means for scanning the pattern and sampling each scanned line at a predetermined length to convert the pattern into digitally coded patterns . a rotary means rotates the two - dimensional pattern relative to the converting means to attain uniform spatial distribution of the two - dimensional pattern . a discriminating means discriminates that the digital coded patterns corresponding to the contour line segments placed between the neighboring scanning lines correspond to the number of times the length of the sample to classify the segments into a number of groups according to the result of the discrimination . a computer multiplies the outputs from the classifying means by predetermined weighting coefficients , respectively , at each rotated position of said two - dimensional pattern to obtain the average of the contour length of the two - dimensional pattern at every rotated position .