To provide high-quality conversion images by suppressing disturbance of the shape of a character due to pixel number conversion.

A pixel number converter 1 includes: a line width conversion table preparation unit 3 for preparing a line width conversion table 3c for specifying the line width (conversion line width) of a black line on the conversion image corresponding to the line width of the black line of an original image on the basis of a conversion magnification; and a conversion processing unit 4 for changing the line width of the black line present in the original image by using the line width conversion table 3c and generating the conversion image. The conversion processing unit 4 includes: a distal end coordinate detection section for detecting the coordinates of the distal end pixel of the black line within the original image; a black line length detection section for detecting the length of the black line; a conversion distal end coordinate calculation section for calculating the coordinates on the conversion image corresponding to the detected coordinates; a line width acquisition section for acquiring the conversion line width corresponding to the detected length of the black line by using the line width conversion table 3c; and a line unit conversion section for preparing, on the conversion image, the black line whose start point is the coordinates calculated by the conversion distal end coordinate calculation section and which has the length of the conversion line width acquired by the line width acquisition section.