PURPOSE: To decrease the labor and the time needed for checking by holding a prescribed width at the dot data of an original picture and the vector data read from a recognizing result file and calculating and outputting the difference in the dot data.

CONSTITUTION: An original image file 1 accommodates the dot data of an image read by using a scanner, etc. A recognizing result file 2 accommodates the vector data of the recognized data corresponding to the read image data. A dot preparing device 3 prepares the dot data of a mode to thicken the segment of vector data read from a recognizing result file 2. A logical arithmetic device 4 calculates and outputs the difference between the dot data of the original image read from the original image file 1 and the dot data of the mode read and thickened from the recognizing result file 2. The area, in which the difference exists, shows the place with a high possibility that the recognizing result is erroneous, the area to execute the checking is limited and the checking can be rapidly executed.