  We study the possibility that the scalar mesons exist as four-quark states.
The energy shift of two pseudoscalar mesons as a function of spatial lattice
size makes a distinction between bound states and scattering states of
four-quark states. We calculate the four-quark state in the quenched
approximation, ignoring the two-quark annihilation diagrams and the vacuum
channels. We perform a calculation of pseudoscalar meson scattering amplitudes,
using N_f=2 Wilson fermion and plaquette/Iwasaki gauge actions. We obtain the
indication that the four-quark states in the case of the isospin zero (I=0) and
two (I=2) channels are no bound states. And we find that the bound energy
depends strongly on pion mass rather than the ratio of pion mass to rho meson
mass.
