  We show how parametric resonance mechanism follows quench mechanism in the
classical linear sigma model. The parametric resonance amplifies long
wavelength modes of the pion for more than $10 fm/c$. The shifting from the
quench mechanism to the parametric resonance mechanism is described by a time
dependent quantity. After the quench mechanism is over, that quantity has an
oscillating part, which causes the parametric resonance. Since its frequency is
$2 m_\pi ~(m_\pi$ : pion mass), very long wavelength modes such as k = 40 MeV
of the pion are amplified by the parametric resonance.
