PURPOSE: To prevent error printing, in a printing apparatus such as an impact line printer, by detecting whether the address of character code memory is read or not in predetermined order.

CONSTITUTION: When printing scanning comprising five sub-scannings is performed at every one character pitch movement and the comparison of a character code of every fifth number and printing data of every sixth figure is performed during a sub-scanning period, the output of a code address counter 5 is coincided in lower rank two bits in each sub-scanning. Therefore, lower rank two bits of the value of a character position counter 4 loaded to a flag counter 24 by a clock pulse generator 25 generating one pulse in starting sub-scanning and lower rank two bits of the code address counter 5 loaded by the character mark signal in the sub-scanning are compared by a comparator 26 to make it possible to prevent error printing.