When transfer of a data frame from a host computer delays during image printing using data transferred from the host computer, a sequence controller (203) determines that generation of print data does not catch up with image printing and a time delay is generated in image printing. A data processor (201) divides a data frame (DF) transmitted immediately before generation of the time delay into overlapping data c and the remaining data a. The data processor further divides the overlapping data c into two overlapping data c.sub.1 and c.sub.2. The data c.sub.2 is extracted from the data frame (DF), held by an overlapping data holding unit (205), and added to the start of the first data frame (DI) transmitted after generation of the time delay. In this manner, when data transfer is left undone during image printing and a printing time difference is generated in image printing, part (c.sub.2) of image printing before generation of the time delay is performed after the time delay, suppressing image degradation.