  We derive some consistency conditions for fivebrane in M theory on R^5/Z_2
orbifold from the quantization law for the antisymmetric tensor field. We
construct consistent fivebrane configurations in R^5/Z_2 type orbifold that
exhibit the correct low energy dynamics of N=2 SQCD in four dimensions with
symplectic and orthogonal gauge groups. This leads us to propose the M theory
realization of orientifold four-planes of various types, and we study their
properties by applying the consistency conditions.
