PURPOSE: To perform an effective recovery heat control at the time of expressing multiple gradations by counting printing data by multiplying it by a function, and performing the recovery heat control.

CONSTITUTION: If image information which is output from a memory (a) for temporarily storing the information input from a user interface has, for example, 3-bit length, a TPH1/Fb converts 3-bit length image information to a pulse responsive to the data amount, applies a TPHc to perform a printing. In this case, the image information is converted by FUN, ROMd to a value by considering the degree of heat storage to provide its linearity. A correction is conducted by the conversion at the times of low and high densities, the linearity of applied recovery is raised, thereby performing a preferable thermal control. An ADDERe counts the history of application of dots conducted in the TPHc, and transmits the result to the TPH1/Fb.