The present invention provides an image compensating device for a joint display. The image compensating device includes a light incident surface, a parallel light emitting surface, and a plurality of light guiding channels extending from the light incident surface to the light emitting surface. The light emitting surface of image compensating device is greater than the light incident surface. The section area of each light guiding channel is gradually increased from the light incident surface to the light emitting surface, by which to extend the image provided by the peripheral region of each cell of the joint display and provide a seamless joint image.