A first image producing program perspectively transforms each polygon in a virtual space onto a plane on the basis of a view position in order to produce a first image, and a second image producing program deteriorates a quality of the first image to produce the second image having the same size as the first image. A synthetic image producing program produces a display image with combination of the first and second images by applying semi-transparentizing processing to at least one of both first and second images so that each polygon of the first image can be displayed around a depth position of a gaze position and each polygon of the second image can be displayed as the polygon approaches at least one side of both front and rear sides concerning the gaze point.