In an image data processing device, correcting of input color image data, converting the input data to monochrome image, and judging whether the image expressed by the input color image data is a color image or a monochrome image, are all performed simultaneously; the corrected color image data and the converted monochrome image data are stored; and based on the judgment, any one of the color image data and the monochrome image data stored are transmitted to an external device via a communicating unit.