PURPOSE: To constitute information of print quality characteristic easily and to enable easy modification thereof by providing matrix terminals to the flat cable at the print section of a printer and providing solder pat portions at the cross points of the matrix circuit thereby representing the print quality characteristic with combination of soldering.

CONSTITUTION: Matrix terminals 8-10 are provided to a flat cable 6. Resistances of head are ranked and combination of solder pad portions 11, 12 at the cross points of a matrix circuit is determined. Combination of matrix for every rank is stored in a circuit board, and a driving pulse necessary for obtaining optimal print density is set for each rank. When a head is connected with the circuit board, a signal is fed from the matrix section to the input terminal of a microprocessor then the rank is determined and the driving pulse is set by means of the microprocessor thus carrying out printing operation. By such arrangement, fluctuation of the resistance of the head is corrected automatically and uniform print density can be obtained for any rank head.