PURPOSE: To provide a device for effectively performing these multiple processings concerning the image processor to perform communication processing or the like parallelly to image processing for reading image information from a check or the like and displaying or printing this information.

CONSTITUTION: This image data processor provided with an image read part 1 to scan a source image, to read the image for the unit of one picture element and to prepare image data, CPU part 3 to perform processing such as the storage of image data read by the image read part 1 parallelly to the processing of communication control with a host computer, and bus 5 to transfer data between these CPU part 3 and memory part 2, is equipped with an image memory part 6 connected to the bus independently of the memory part 2 for storing image data, and bus switch part 7 to disconnect this image memory part 6 from the bus 5 when storing the image data read by the image read part 1 in the image memory part 6.