  We study the effect of one-loop corrections from nucleon together with those
from boson in the massless chiral sigma model, where we perform the
Coleman-Weinberg renormalization procedure. This renormalization procedure has
a mechanism of spontaneous symmetry breaking due to radiative corrections in
$\phi^4$ theory. We apply it to the system of nucleon and bosons with chiral
symmetry where the negative-mass term of bosons does not exist. Spontaneous
chiral symmetry breaking is derived from the contribution of nucleon and boson
loops which generates the masses of nucleon, scalar meson, and vector meson
dynamically. We find that the renormalization scale plays an important role for
the breaking of the symmetry between fermion (nucleon) and boson, and
eventually for the chiral symmetry at the same time. In addition, we find that
the naturalness restores by means of the introduction of the vacuum fluctuation
from both nucleon and boson. Finally we obtain a stable effective potential
with the effect of Dirac sea in the chiral model for the first time.
