Thermal printing is conducted as follows generally-used small-width thermal heads having an effective width equal to the width of A-4 size paper or B-4 size paper are arranged in rows, each of which has a plurality of thermal heads, over two parallel platens extending at right angles to the direction in which the recording paper is moved, in such a manner that the thermal heads in different rows are alternately in the direction of the width of the recording paper, whereby the heating resistors in the thermal heads in different rows overlap one another with respect to the direction in which the recording paper is moved.
