  We quantize the topological $\sigma$-model. The quantum master equation of
the Batalin-Vilkovisky formalism $\Delta_\rho \Psi = 0$ appears as a condition
which eliminates the exact states from the BRST invariant states $\Psi$ defined
by $Q \Psi = 0$. The phase space of the BV formalism is a supermanifold with a
specific symplectic structure, called the fermionic K\"ahler manifold.
