PURPOSE: To simplify the driving circuit of a thermal head and to obtain a print data with high quality by controlling power of a heating resistor only when a down-counter counts down a given data signal so as to control the power application time digitally.

CONSTITUTION: A time when a base of an output transistor (TR) 4 is at "0" level by a count data value inputted to the down-counter 1 in other words the power application time to the heating resistor is controlled and it is also possible to control the power application time to the heating resistor depending on the pulse period and the count data value by varying the pulse period of the clock pulse. In this case, the period to make an output terminal 14 to "0" level is (n× T), where (n) is the count data and T is the clock pulse period, lots of gradations are obtained and a gradation recording data having always stable print density and with constant quality independently of ambient temperature by controlling the period of the clock pulse in matching with the thermal head ambient temperature condition.