PURPOSE: To reduce the number of read of memory, provide enough time, use low speed memory, and reduce the cost by providing a primary recording memory for storing energization time information to heating elements for at most one line, a circuit for changing information orders and rearranging, and a gradation comparing circuit.

CONSTITUTION: Data 41 meaning energization time of each heating element 58 is inputted to a primary recording memory 43 for one line through a data order rearranging circuit 42. When a transfer to the primary recording memory 43 is completed, an address generating circuit 53 is reset so as to start a processing from a lower byte of a first information group. An output of a gradation count circuit 45 is inputted to one input of gradation comparing circuits 44 and 4 bits out of an output 46 of the primary recording memory 43 are inputted to other input. When the output 46 of the primary recording memory 43 is larger or equal, an energization enabling signal 47 is outputted. Two gradation comparing circuits 44 are provided so as to convert one output 46 from the primary recording memory 43 into two energization enabling signals 47 and 48.