PURPOSE: To obtain high quality printing of half dot constitution at a high printing speed, by a method wherein the interval of dots in a lateral direction is set to a 1/2 dot pitch and, when separate dots to be printed are present within a 3/2 dot pitch from the dots printed by the printing element of one printing row, printing is performed by the printing element of the other printing row.

CONSTITUTION: When the a-rows of the fifth pin and the seventh pin are printed by a left printing row L, and the e-rows of the fifth pin and the seventh pin are printed by a right printing row R, since the f-row of the seventh pin is printed by the right printing row R and presents within a 3/2 dot pitch with respect to an e-row, said f-row is printed by the left printing row L. Therefore, the fifth pin and seventh pin of the right printing row R are driven in a step 3 to print a part of a d-row, and the seventh pin 7 of the right printing row is driven in a step 10 to print a part of the f-row. By this constitution, the min. interval wherein the same printing element of the same printing row is driven becomes four steps of a carriage 4, that is, a two- dot pitch. By this method, the response frequency of a printing head can be delayed by 1/2 and to the one-dot pitch running of the carriage and, when the response frequency of said head is supposed to be the same F, the running of the carriage can be increased to two times.