Among twelve lines indicating a 3D space (Ad) (X-axis direction lines (Xa)(Xb)(Xc)(Xd), Y-axis direction lines (Ya)(Yb)(Yc)(Yd), Z-axis direction lines (Za)(Zb)(Zc)(Zd)), display colors of red (R), green (G) and blue (B) are allocated to three lines (three-dimensional directions), i.e. an X-axis direction line (Xa), a Y-axis direction line (Ya) and a Z-axis direction line (Za), which have, as starting points, a 3D space minimum point (M) at which each of an X value, a Y value and a Z value becomes minimum, and red gradation display (Rgr), green gradation display (Ggr) and blue gradation display (Bgr) (first origin direction distinct display) are executed such that the colors become darker toward an origin (O) of the 3D space (Ad) and become lighter away from the origin (O).