PURPOSE: To miniaturize the title thermal head by making a strobe signal useless by lessening a control signal wire and by making a gate circuit needless, by a method wherein a transfer speed of an image signal is suitably selected, and a direct heating resistor is driven by the image signal in a shift register.

CONSTITUTION: Since an image signal (in) is transferred in a shift register 1 by a clock signal (clk) and each bit is connected directly to a transistor TR1WTR6 driving a heating resistor R1WR6, an output signal (a) of a flip-flop Q1 becomes '1' and the transistor TR1 immediately turns ON. This state continues until three clock signals (Clk) enter. Though the heating resistor R1 is heated during that period, heat sensitive paper can not be colored by selecting frequency of the clock signal (clk) at a sufficiently high level. An output signal (b) of a flip-flop Q4 becomes '1' when a fourth clock signal (clk) comes, and immediately turns ON. The heating resistor R4 is heated to a temperature at which the heat sensitive paper is colored. Therefore, by controlling a line speed of the image signal (in), uniform density can be obtained over a broad range of temperature.