  We study the possibility of family unification on the basis of SU(N) gauge
theory on the 6-dimensional space-time, $M^4\times T^2/Z_N$. We obtain enormous
numbers of models with three families of SU(5) matter multiplets and those with
three families of the standard model multiplets, from a single massless Dirac
fermion with a higher-dimensional representation of SU(N), through the orbifold
breaking mechanism.
