  We study M5-brane configuration of the chiral gauge theory whose Type IIA
brane configuration with orientifold 6-plane(O6) is studied by various authors.
Much of the paper is devoted to studying M-theory picture of SO/Sp gauge theory
with fundamental flavors realized in Type IIA setup with O6-plane. The Higgs
branch of N=2 SO/Sp gauge theory is studied and the curve corresponding to
rotated brane configuration is presented. In the chiral gauge theory, the
middle NS$^{\prime}$5-brane on top of the O6 plane is realized as a detached
rational curve. Depending on a location of the rational curve in $x^7$
direction, the same curve plus the rational curve can be interpreted as
describing the Coulomb branch of $SU(2N_c)$ chiral gauge theory,
$SO(2N_c)/Sp(N_c)$ gauge theory with $N_f/(N_f+4)$ fundamental hypermultiplets.
Various consistency checks for this proposal are made. By introducing two more
rational curves corresponding to NS$^{\prime}$5-branes, one can produce a
non-trivial fixed point which mediates chiral non-chiral transition.
