1. An image observation device having a glass piled half mirror, for observation of a plurality of images in superposition to each other, said half mirror including two transparent bodies of equal optical property and substantially equal thickness constituting both side portions thereof sandwiching a half mirror surface therebetween, said plurality of images being disposed in symmetry with respect to a plane of symmetry constituted by said half mirror surface, and a pair of light source boxes disposed in symmetry with respect to said plane of symmetry, each box being adapted to hold one image plate producing one of said plurality of images and having a light source therein and a filter thereon, said filters being of different colors complementary to each other, said light sources being adapted to illuminate said image plates through said filters.