PURPOSE: To improve picture quality by outputting picture information as they are when the inputted picture information are composed of density information and position information, and outputting the picture information while converting them to picture information composed of the density information and the position information when the picture information composed of the density information only.

CONSTITUTION: Picture data to be sent from a host device are inputted for each picture element information of an attention picture element and when picture element information in the inputted picture information are already composed of the density information and the position information, the picture element information are supplied to a printer, for example, as they are. When the picture element information are composed of the density information only, from the density information of the picture elements around the attention picture element, the position information are generated concerning a position, where the attention picture element is printed in one picture element area, and supplied to the printer while converting to the information combined with the density information at a picture data conversion part 2. Thus, the picture element with the high quality can be obtained without damaging gradient at a half tone picture and the picture can be obtained without making an uneven part apparent to be generated by an oblique line part or a curve part at a linear picture such as a character or a graphic, etc.