PURPOSE: To increase of the speed of longitudinal printing, by a method wherein a lateral operating process and a longitudinal operating process are exchanged according to the received result of alterating instruction of processing system and the printing operation is controlled.

CONSTITUTION: If there is the instruction for alteration of processing system by checking the state of processing system alteration instruction switch 108, a microcomputer 91 sets a processing system alteration flag F to F=1. Further in the absence of processing system alteration instruction, it resets the flag F to F=0. As to the processing system alteration instruction, for instance the processing system alteration setting instruction is sent as a code of 'ESC+a' and the processing system alteration release instruction is sent as a code of 'ESC+b'. Firstly, whether the received data is a 'ESC' code or not is determined. If it is the 'ESC' code, the next receiving data is read from a receiving buffer. If 'a', the flag F is set to F=1. If not 'a', whether it is 'b' or not is determined. Then, if 'b', the flag F is reset at F=0 and if not 'b' also, the other ESC command process is executed. Then, if the received data is not 'ESC' code, the code process corresponding to each command is executed. The space direction (transversal) operation process and the line feed (longitudinal) operation process are exchanged according to processing system alteration instruction result for each code and the printing is controlled.