PURPOSE: To obtain a character pattern not deteriorated in quality even when decoration processing containing rotation is performed, by a method wherein all of dot patterns are stored at the first density among the longitudinal and lateral direction densities of an output means and subjected to decoration processing to be converted to the longitudinal and lateral densities of the output means.

CONSTITUTION: A character pattern memory means 1 stores a pattern at density of 1/360" in both of longitudinal and lateral directions because an output means 4 can not output two dots of the max. density wherein longitudinal and lateral densities are respectively 1/360" but continuous. A rotatory processing means 2 applies operation for rotating a character pattern if necessary to output said pattern and a density altering means 3 alters the character pattern to the possible output density of the output means 4. For example, in the character pattern store in the memory means, all of patterns are 1/360" density corresponding to the longitudinal and lateral densities of the output means 4. Now, this pattern is rotated by 90° to the left and subsequently altered in density to obtain a pattern processed so that two continuous dots are not continued in the laterial direction. Even in this case, the thickness of a line and the quality of an oblique line are not almost changed.