PURPOSE: To enhance the contrast of character and line drawing data, which is converted from two-valued ones to multiple tonal ones, by a method wherein at least image element values near the minimum tonal value in the character and line drawing data is raised in a contrast converting method of multiple tonal character and line drawing.

CONSTITUTION: Character and line drawing data are produced by representing the two-valued representation of the original image data in the multiple tonal data or high resolution character and line drawing data consisting of two-valued data in two values, which are the minimum value 0 and the maximum value 255 among multivalued data obtainable, so as to be recorded in a first recording medium 10 as the original image data. Image element values of data written from the recording medium 10 is tabularly converted through a tabularly converting means 14 by employing the predetermined conversion table 12 so as to contrast-convert the character and line drawing data. Concretely, the image element values near the minimum value and/or the maximum value of the multiple tonal data are processed to be raised. The character and line drawing data after the contrast conversion is stored in a second recording medium 16.