Observed Property of sigma-Meson and Chiral Symmetry

The phenomenologically observed property of sigma(600) in our recent analyses of various pi pi-scattering and -production processes is reviewed and compared with the prediction of SU(2) linear sigma model. Furthermore, a possibility of the scalar sigma-nonet (sigma (600), kappa (900), f_0(980) and a_0(980)) forming with the pseudoscalar pi-nonet a linear representation of SU(3) chiral symmetry is investigated. The origin of repulsive background phase shift delta_BG, which is essential to lead us to the sigma-existence in our phase shift analysis, is shown to come from the repulsive lambda phi^4 interaction.