1. A three-dimensional image calculating method for calculating a plurality of images utilized in a three-dimensional image display device which comprises: a lens array having the predetermined number of convex lenses arranged in a matrix; and image display means for displaying a plurality of images corresponding to the respective convex lenses, wherein said method consists of steps of: assuming a referential viewing distance wherefrom a reproduced three-dimensional image is viewed; dividing a viewing zone positioned at said referential viewing distance (a referential viewing area) into small areas arranged in another matrix; ray tracking along a line connecting the center of said small area with a base point of a selected convex lens; determining a first cross point of said line connected with said selected lens to surfaces of objects to be displayed as a three-dimensional image; calculating image information on said first cross point; repeating said calculating step on the whole convex lenses; and repeating steps from said ray tracking to just prior step to the present step on respective said small areas.