1. A game system for projectively transforming a plurality of polygons, which form three-dimensional object located in an imaginary three-dimensional space, to a viewpoint coordinate system to draw the polygons on a projection plane, comprising: a polygon drawing means for drawing a polygon with a first texture which affects drawing of other texture; a second texture drawing means for drawing a second texture, prepared in advance, on the polygon drawn by the polygon drawing means based on two-dimensional coordinates of the second texture; and a texture moving means for simulatively moving the second texture, drawn by the second texture drawing means, on the polygon drawn by the polygon drawing means by varying the two-dimensional coordinates in time-series.