  We investigated numerically properties of Nambu monopoles in lattice
Electroweak theory at realistic values of $\alpha$ and $\theta_W$. Our choice
of parameters of lattice Lagrangian corresponds to large values of the Higgs
boson mass $M_H > 2 M_W$.
  We find that the density of Nambu monopoles cannot be predicted by the choice
of the initial parameters of Electroweak theory and should be considered as the
new external parameter of the theory. We also investigate the difference
between the versions of Electroweak theory with the gauge groups $SU(2)\otimes
U(1)$ and $SU(2)\otimes U(1)/Z_2$. We do not detect any difference at $\alpha
\sim {1/128}$. However, such a difference appears in the strong coupling region
and is related to the properties of monopoles constructed of the hypercharge
field.
