  We have investigated neutralino dark matter in the framework of minimal
supersymmetric Standard Model focusing on the coannihilatioin region. In this
region, where the particle whose mass is tightly degenerated with the
neutralino dark matter exists, we can solve the Lithium problem in the case of
lepton flavor being violated. It turns out that Sommerfeld enhancement is
important in the coannihilation region so that the dark matter signal becomes
large enough to be observed by the current sensitivity of indirect experiments.
