  A new dynamical symmetry breaking of $SU(2)_{L}\times U(1)$ caused by the
combination of the axial-vector component and the fermion mass is found in
electroweak theory. We obtain (m^{2}_{W}={1/2}g^{2}m^{2}_{t}) and
(m^{2}_{Z}=\rho m^{2}_{W}/cos^{2}\theta_{W}) with (\rho\simeq 1), (G_{F}={1/2
\sqrt{2}m^{2}_{t}})}}). Two fixed gauge fixing terms for W and Z boson fields
are dynamically generated. Massive neutrinos are required.
