PURPOSE: To measure quantitatively the horizontal dislocation of dots in a line by regarding a line of the dots constituting a group as a straight line and measuring and evaluating the width and intervals of the line by an image processing apparatus.

CONSTITUTION: A key board is operated to drive an apparatus, an image processing program containing a memory 3 for an image processing program from CPU 5 is executed, and a line of dots on a print which is photographed by an image input CCD camera 1 is inputted into an A/D conversion part 2 as video signals. In the A/D conversion part 2, the video signals are converted into numerical data indicating light and shade levels, and the numerical data are stored in a frame memory in which each address of the memory is allocated to one picture element. The width, central position, etc., of a line are calculated by CPU 5 with the use of the numerical data indicating light and shade levels which are read out from the frame memory 4, the image processing program stored in the memory 3, and an operation memory. The calculation results are outputted from an output apparatus 6.