PURPOSE: To constantly perform high quality recording while maintaining the temperature of a head substrate board at a level lower than a fixed value, by controlling the thinning-out ratio of picture signals and the width of head-driving pulses on the basis of the temperature rise of a heat sensitive recording head.

CONSTITUTION: When the temperature of a substrate board exceeds a fixed value, an output signal S3 from a comparator 9 is changed into an "H" level by a signal from a thermistor 8 attached to the substrate board of a heatsensitive recording head 3, and an electromagnetic switch 10 is turned into an ON state to change the time constant of a timer 11. Consequently, the width of the resultant outputted driving pulse S4 is changed, and a picture signal SB inputted from a gate G1 is outputted as a signal S2 thinned-out every bit at the same time. As a result, when the temperature of the head substrate board exceeds the fixed temperature, both of the width (electric power) of the driving pulse and a line density are lowered, and the temperature of the head substrate board falls at a level lower than the fixed value with high responsiveness.