  The brane world based on the 6D gravitational model is examined. It is
regarded as a higher dimensional version of the 5D model by Randall and Sundrum
>. The obtained analytic solution is checked by the numerical method. The mass
hierarchy is examined. Especially the {\it geometrical see-saw} mass relation,
between the Planck mass, the cosmological constant, and the neutrino mass, is
suggested. Comparison with the 5D model is made.
