PURPOSE: To eliminate the deviation of printing by nullifying the signal of dot pulse only during the peirod when printing is deviated by play of the mechanism when printing is made in reversed direction.

CONSTITUTION: The moving speed of printing head in the space direction is accelerated by preliminary running in the rising part at the time of start in the section T1, restored to its steady speed in the section T2, and then decelerated and stopped in the section T3. Printing is made within the section Tp in the section T2 so that the intervals of dots are kept constant. The section T2 corresponding to the first one place at the printing time in the reverse direction is for correction for deviation. After the printing head 5 is moved to te right direction, a delivery screw 3 is reversely turned in the direction of arrow a3 and reversely direcred dot pulse begins to generate. But, the printing head 5 does not move reversely due to the play X of sliding portion, etc. Thus, dot pulse generated in the section is nulified and the deviation of printing is prevented.