1. An apparatus for displaying three-dimensional objects in two dimensions comprising: environmental data memory means for storing form and position data of a plurality of three-dimensional objects; input means of selecting two three-dimensional objects of said plurality of three-dimensional objects; means for reading out form and position data of the selected three-dimensional objects from said environmental data memory means; means for computing a line-of-sight vector for displaying the selected three-dimensional objects as two-dimensional figures with no interference therebetween in accordance with the form and position data that are read out from said environmental data memory means; means for calculating two-dimensional figure data for the selected three-dimensional objects in accordance with the form and position data read out from said environmental data memory means and the line-of-sight vector computed by said line-of-sight computing means; and means for displaying the selected three-dimensional objects as two-dimensional figures in accordance with the two-dimensional figure data calculated by said calculating means.