PURPOSE: To form an image based on an image signal with high reproducibility in spite of the change of sensitivity characteristic by environment received by a recording material.

CONSTITUTION: The image signals converted to three colors of Y, M, and C are outputted to a line buffer 182 via a correction LUT 180 and a resistance value correction table 181 for dispersion correction, and energy is attached on it by a thermal head 32, and the image is recorded on a thermosensitive recording material. The correction LUT 180 is rewritten by an arithmetic part 186. An infrared reflection sensor 130 which detects a moisture content, a reference LUT 188 which stores a reference LUT, and a coefficient storage part 190 which stores a correction coefficient K in accordance with a detected moisture content ratio are connected to the arithmetic part 186, and the reference LUT 188 is multiplied by the correction coefficient K for the detected moisture content ratio, and is rewritten to the LUT whose sensitivity characteristic is corrected. Therefore, the energy in which the sensitivity is corrected corresponding to the moisture content ratio of the thermosensible recording material can be attached when heating processing is applied to each dyestuff layer.