  We analyze the mixing nature of the low-lying scalar resonance consisting of
the pipi composite and the elementary particle within the sigma model. A method
to disentangle the mixing is formulated in the scattering theory with the
concept of the two-level problem. We investigate the composite and elementary
components of the sigma meson by changing a mixing parameter. We also study the
dependence of the results on model parameters such as the cut-off value and the
mass of the elementary sigma meson.
