An image combining apparatus, which is connected with a white-board device, and an image projecting device, includes an image outputting section for outputting the projective image data to the image projecting device, an operation section for designating any position on a projected image, an image processing section for generating projective image data for displaying a mark, a memory section for memorizing the coordinate positions of two or more standard points, and an image inputting section for receiving the scanned image data from the white-board device, wherein the image processing section obtains the coordinate positions of the certain marks when the two or more standard points have been designated, the image processing section makes correspondence with the coordinate positions of the certain marks and the coordinate positions of the two or more standard points respectively, whereby the image processing position recognizes the position of the projected image on the viewing surface.