PURPOSE: To enable fixed printing quality to be maintained by providing means for measuring the gap between a printing head and for moving the head so as to adjust the gap to a desired value.

CONSTITUTION: A main controlling part 3 causes a reflection-type sensor 2 to output an output signal from an emitting part so that the signal is reflected by a platen 4. A signal returned by reflection is received by a receiving part of the sensor 2, and is fed back to the main controlling part 3. The main controlling part 3 detects the distance between a printing head 1 and the platen 4 based on the emitted signal and the feedback signal, and operates a motor 5 to move the head upward or downward until the distance becomes equal to a desired platen gap. By this, the gap between the head 1 and the platen 4 is corrected, and the spacing therebetween can be maintained at a constantly fixed value.