To suppress generation of jaggy with respect to an oblique line or a contour except a prescribed angle by judging the outline of an object in a picture or the direction of a line from a binary picture, executing interpolation in the judged direction and catching features of an outline belonging to an original picture of faithfully execute interpolation.

A binarizing circuit 1 binarizes the original picture and a direction judging circuit 2 digitizes an oblique line included in a picture and the angle of an oblique outline at the object. Then, the kinds of the angles of the oblique line are four kinds being 22.5° lower left, 45° lower left, 45° lower right and 22.5° lower right with respect to a horizontal direction, e.g. A correlation circuit 3 interpolates pixels in accordance with the output of a direction judging circuit 2 and executes simple internally dividing processing. A converter of the number of pixels can obtain an interpolated picture free from jaggy by binarizing the original picture, deciding a direction to be interpolated from the binarized picture and executing interpolation processing in a direction to be interpolated based on the judging result.