1. A game machine, comprising: field producing means for setting a three-dimensional virtual space where world coordinates are set in a memory and for producing a field which is comprised of two or more stages connecting with each other on said world coordinates, in said each stage, a character density is individually set; character locating means for respectively locating two or more characters appearing in a game in said stages in said field; operation character locating means for locating an operation character operable by a player through a controller in said stages of said field; character locating means for respectively locating characters excluding said operation character which appear in a game world on said stages on said field; a number of said characters to be located on said field by said character locating means being lower than a number of said characters necessary for keeping a predetermined character density which is set on each of said stages so as to be simultaneously satisfied in all stages; character density computing means for computing a character density in said stage where said operation character is located; character density judgment means for judging as to whether or not said computed character density is lower than a predetermined character density which was set for said stage; short character number computing means for computing a number of short characters when said character density was judged to be lower than said predetermined character density; short character extracting relocation means for extracting a number of said characters which corresponds to said computed number of short characters from one or more of said stages where said operation character is not located, and for relocating said extracted characters in said stage where said operation character is located; and image display means for displaying an image of said stage where said operation character is located on a monitor; whereby even if the total number of said characters in said field does not reach a number of said characters with which said character densities of the respective stages of the whole field can be simultaneously satisfied, characters are exchanged between said stage where said operation character is located and the other stages so as to produce a result as if said character density is satisfied in all stages with small computational load.