PURPOSE: To realize uniform thermal half-tone recording of high quality by controlling energy applied to heating elements corresponding to respective dots of picture elements to be printed according to the ratio of print energy and heat accumulation states of the heating elements.

CONSTITUTION: Received image information is stored in the 1st buffer 11 and the 2nd buffer 12 at intervals of two lines as a half-tone image corresponding to one of nine gradations. The outputs of those buffers are applied to the 1st operator 20 consisting of a Zi operator 21 for calculating a heat accumulation state level Zi and a Zi/f converter 22 for converting the heat accumulation state level into a state coefficient (f), and the state coefficient (f) is outputted to the 2nd operator 40 as a result of the arithmetic. Image information from the 1st buffer 11, on the other hand, is converted to one of nine kinds of pulse width in a pulse width storage table 30 and applied to the 2nd operator 40. The 2nd operator 40 processes those two inputs to calculate the width of a pulse to be applied to each fine picture element.