We have found novel perceptual phenomena for developing a three-dirnensional(3-D)display by using only two 2-D images displayed at different depths. It enables an observer using no extra equipment to perceive an apparent 3-D image of continuous depth when the luminance is divided between the two 2-D images according to the 3-D image depth. We have also developed a prototype 3-D display by applying the phenomena to several 2-D images. It can easily produce moving 3-D color images by using color conventional 2-D displays.