To reduce production costs by sharing a buffer memory for preceding line reference by providing an image data storage area for one line at least to be commonly referred to as preceding line data by a high picture quality reading processing means and a smoothing means.

A gate array 7 consists of the high picture quality reading processing means for performing high picture quality reading processing for reading a half tone image and the smoothing means for performing smoothing processing for smoothing the outer edge of a recorded image. A buffer memory 10 consists of a storage means having the image data storage area for one line at least to be commonly referred to by the high picture quality reading processing means and the smoothing means as the preceding line data. Thus, since the image data storage area for one line at least in the buffer memory 10 is shared by high picture quality reading processing and smoothing processing, the waste of image data storage areas can be saved and production costs can be reduced.