PURPOSE: To perform printing at a proper position even if the lateral shift, oblique running or meandering of an actual slip is generated.

CONSTITUTION: An image processor has an image signal generation means generating the image signal corresponding to a slip image, a side detection means 17 detecting one of the right and left sides of an actual slip on the basis of the image signal and a printing part 16 correcting a printing position on the basis of one of the detected right and left sides to determine an actual printing position. In this case, since a printing position is corrected on the basis of the distance between the detected right or left side and the set right or left side set to the image processor, even when the lateral shift of the actual slip is generated, printing can be performed at a proper position.