  We study the $K \to 2 \pi$ decays using the $U_L(3) \times U_R(3)$ version of
the Nambu-Jona-Lasinio model with the effective $\Delta S = 1$ nonleptonic weak
interaction. The $\Delta I = {3/2}$ amplitude is in reasonable agreement with
experimental data. On the other hand, the calculated $\Delta I = {1/2}$
amplitudes strongly depend on the mass of the low-lying scalar-isoscalar
$\sigma$ meson, and therefore give a strong constraint on the parameters of the
model.
