PURPOSE: To improve the yield of thermal printer by outputting the value of an average resistance value of a unit heat generating element to the side of a recorder one by one to make the heat generated therefrom adjustable according thereto.

CONSTITUTION: A thermal head 15 is measured in the average resistance value of a unit heat generating element before shipped and calssified in terms of switches 18-1W18-3 according to the resistance value. Then, the switch information is turned to resistance value information with a decoder 32 and a pulse width computing unit 28 determines the print record pulse width by heat storage information from a heat storage state computing unit 26 and the output of a pulse width memory 29 in which each of pulse width one line before is stored and feeds a pulse width signal 34 determined individually for each unit heat generating element to a pulse voltage application circuit of the thermal head. This enables the adjusting of the heat generated from the unit heat generating element according to the average resistance value thereof to improve the yield of the thermal head thereby extending the life with a higher reliability through appropriate control of heat generation.