1. A printer for printing onto a print medium by moving a carriage having a print head alternately in a main scanning direction and a sub scanning direction, comprising: image processing means for generating bit image data by executing predetermined image processing on digital image data inputted from outside; first image data storing means for storing said bit image data; data volume determining means for determining whether or not the volume of said bit image data corresponding to images printed during one main scanning of said carriage exceeds the maximum memory capacity of said first image data storing means; storage control means for storing said bit image data in said first image data storage means when said data volume determining means determine that the volume of said bit image data corresponding to images printed during one main scanning of said carriage does not exceed the maximum memory capacity of said first image data storing means, and for providing a part of said digital image data necessary for (printing) to said image processing means without using said first image data storage means when said data volume determining means determine that the volume of said bit image data corresponding to images printing during one main scanning of said carriage exceeds the maximum memory capacity of said first image data storing means; and second image data storage means for storing said bit image data corresponding to images printing during one main scanning of said carriage, wherein when said data volume determining means determine that the volume of said bit image data corresponding to images printed during one main scanning of said carriage does not exceed the maximum memory capacity of said first image data storing means, said storage control means store, among the bit image data stored in said first image data storing means, the bit image data corresponding to images printed during one main scanning of said carriage in said second image data storing means, and when said data volume determining means determine that the volume of said bit image data corresponding to images printed during one main scanning of said carriage exceeds the maximum memory capacity of said first image data storing means, said storage control means store said bit e data generated by image processing means directly in said second image data storing means without storing it in said first image data storing means, wherein the image processing means includes: an image resizing means for executing a resizing processing on the digital image data inputted from outside; and an image correcting means for, comparing an image size of the resized digital image data and an image size of the digital image data before the resizing processing, executing a correcting processing on the resized digital image data in a case where the image size of the resized digital image data is smaller than the image size of the digital image data before the resizing processing, and executing the correcting processing on the digital image data before the resizing processing in a case where the image size of the digital image data before the resizing processing is smaller than the image size of the resized digital image data.