To provide an image superimposition processor and an image superimposition processing method and a program for achieving an instantaneous and intuitive transparent view by a simple method without installing any camera on the back face of a shielding object or using any motion parallax.

Image arrangement means arranges a virtual object image on a display screen so that it is overlapped with a corresponding position on the display screen of a boundary calculated by boundary position calculation means. Luminance calculation means adjusts, by referring to luminance data, the luminance of a first section where the virtual object image overlaps with an object on the display screen and the luminance of a second section where the virtual object image overlaps with a background on the display screen so that the order of the magnitudes of the luminance of the object, the luminance of the background, the luminance of the first section and the luminance of the second section satisfies stable transparent view conditions or ambiguous transparent view conditions.