  The pole structure of the low energy $\pi\pi$ scattering amplitudes is
studied using a proper chiral unitarization method combined with crossing
symmetry and the low energy phase shift data. It is found that the $\sigma$
pole position is at $M_\sigma=470\pm 50MeV$, $\Gamma_\sigma=570\pm 50MeV$. The
existence of the virtual state pole in the IJ=20 channel is reconfirmed.
Various threshold parameters are estimated and are found in general in good
agreement with the results obtained from the Roy equation analyses.
