Abstract: There is provided an image processing apparatus by which images sent from different modalities are simultaneously displayed on one monitor, such that even when at least one monochromatic image is displayed together with at least one color image, the at least two images can be easily reproduced to have optimum gradations associated with the images. The image processing apparatus includes an identifying device which identifies types of modalities from which the image data have been sent, a correcting device which applies look-up tables or correction coefficients for gradation corrections in accordance with the respective modalities to the image data and performs gradation correction corresponding to the characteristic of the monitor on the image data, and a position setting device which sets positions on a display screen of the monitor in which the diagnostic images are to be displayed.