  We study equivalence classes of boundary conditions in gauge theory on the
orbifold $T^2/Z_3$. Orbifold conditions and those gauge transformation
properties are given and the gauge equivalence is understood by the Hosotani
mechanism. Mode expansions are carried out for six-dimensional $Z_3$ singlet
fields and a $Z_3$ triplet field, and the one-loop effective potential for
Wilson line phases is calculated.
