The present application generates an image in which a contour line is drawn about a tuned object A in a virtual three-dimensional space when a part of the tuned object A is overlapped by another tuned object B that is located at a position closer to a virtual screen. When a line width of the tuned object A is greater than a line width of the tuned object B, the line width of a part of the tuned object A that is overlapped with the tuned object B is set as the line width of the tuned object B. On the other hand, when the line width of the tuned object A is less than the line width of the tuned object B, the line width of the part of the tuned object A that is overlapped is set as the original line width of the tuned object A.