An image processor including a memory to store information on the file format and the maximum file size of image data processable by the image processor and image data processable of one or more external devices; a judging device to judge whether image data input to the image processor can be processed by the image processor or one of the external devices in terms of the file format and file size; an image converter; a transfer controller to transfer the input image data to the external device when the input image data cannot be processed by the image processor but can be processed by the external device while transferring the image data to the image converter when the image data can be processed by the image processor; and an output device to output an image based on the image data processed by the external device or the image converter.