PURPOSE: To provide a method for always keeping constant the amount of ink contained in an ink ribbon by a method wherein the amount of ink to be supplied to the ink ribbon is controlled according to the numeric value of printed letters by counting the number of printed letters.

CONSTITUTION: A counter 7 is used to count the number of printed letters by counting the number of the operations of a printing hummer 14. A control circuit 8 is employed to obtain the number of printed letters per unit time based on the number of printed letters counted by the counter 7 and to control the turning speed of a motor 9 so that the speed is proportional to the number of printed letters per unit time. A pump 10 is used to supply the amount of ink proportional to the number of printed letters from an ink cartridge 11 to a nozzle 12, whereas a roller 13 is operated to apply the amount of ink proportional to the number of printing letters to an ink ribbon 1.