1. A method for producing computer generated holograms in a form of holographic video by calculating hologram fringe patterns, comprising the steps of: storing basic patterns for wavefronts of lights from objects; detecting a motion vector of each object to be displayed after a prescribed time; classifying the objects into a plurality of groups according to motions of the objects indicated by the motion vector of each object, such that objects in an identical motion are classified as belonging to an identical group; calculating a hologram fringe pattern for each classified group of objects separately by initially using a corresponding one of the basic patterns and subsequently image processing each calculated hologram fringe pattern; and producing a hologram to be displayed after the prescribed time by synthesizing all separately calculated hologram fringe patterns.