1. An impact judgement device for judging impacts between a moving object moving in an artificial three-dimensional space and a three-dimensional model constituted by a plurality of polygons, the impact judgement device comprising: model storing means for storing the vertex-coordinates of the respective polygons of said three-dimensional model, and impact judging means for performing impact judgement using the movement vector of said moving object and said vertex-coordinates; wherein said model storing means represents said vertex-coordinates by means of central-coordinates being an average value of the maximum value and minimum value of the each of the coordinate components, an expansion factor to be used for achieving prescribed value by multiplication by the difference between the maximum value and minimum value of each coordinate component, and converted vertex-coordinates obtained by subtracting said central-coordinates from the respective vertex-coordinates and then multiplying by said expansion factor; and stores said central-coordinates and said expansion factor in a floating-point value form, and said converted vertex-coordinates in an integer form.