PURPOSE: To expand a high quality character pattern into character pattern at high speed by a method wherein treatments are performed by the variable power, the type face changing treatment and finally the thinning-out treatment in the order named when the variable power of character pattern, the change of type face and the thinning- out treatment of the pattern are pointed respectively.

CONSTITUTION: Character code sent from a host computer 20 and the modify information of character pointed by the character code are stored in a printing device 30. When the printing data stored in the receive buffer 31a of the device 30 is read out under the condition that the data is character code, font data corresponding to the read-out character code is read out of character font 33a and expanded in pattern. For example, when the modification is longitudinally magnifying treatment, the longitudinal magnification of character is carried out. Next, when the formation of italic character is pointed by the modify information, italics are generated. When the generation of script is pointed by the modify information, scrips are formed. By prearranging the modifying order of the character font, the quality of character pattern is prevented from lowering, even when a plurality of character modifications are applied to one another.