PURPOSE: To prevent temperature compensation characteristic from variation in the middle while a sheet of an image is being stored, by a method wherein a regulation means in which a print density is regulated according to a detection output of a temperature detection means is provided, and a recognizing means is operated according to an output of the recognizing means for recognizing delimitation of one picture by a command.

CONSTITUTION: A temperature detection thermocouple 34 is buried in a head unit 20, and a code according to variation of temperature is outputted to D0WD2 with an amplifier 36 and an A/D converter 38. In an OD-V table ROM 40, various kinds of O.D. values for input are so prepared that a drive voltage value of each head to be outputted becomes suitable within each temperature range. An A/D enabling signal is generally made a forbidden state, and a command which will be enabled just before sending data of one picture is sent to a printing side. A temperature of the printer is detected at a temperature at a point of the time, and an optimum correction curve is selected. When a command which clearly identifies completion of one picture is sent, the printer individually varies temperature.