  We report a project to study scalar particles by lattice QCD simulations.
After a brief introduction of the current situation of lattice study of the
sigma meson, we describe our numerical simulations of scalar mesons, $\sigma$
and $\kappa$. We observe a low sigma mass, $m_\pi<m_\sigma\le m_\rho$, for
which the disconnected diagram plays an important role. For the kappa meson, we
obtain higher mass than the experimental value, i.e., $m_\kappa\sim 2m_{K^*}$.
