  We are calculated the expectation value of the axial-vector current induced
by the vacuum polarization effect of the Dirac field in constant external
electromagnetic field. In calculations we use Schwinger's proper time method.
The effective Lagrangian has very simple Lorenz invariant form. Along with the
anomaly term, it also contains two Lorenz invariant terms. The result is
compared with our previous calculation of the photon - Z boson mixing in the
magnetic field.
