Abstract
Solar neutrino observations utilizing tiny cross section of neutrinos have revealed the long-standing "solar neutrino problem." The problem was a breakthrough in measurement of neutrino properties and in new theories beyond the standard particle theory. It has contributed to an evolution of particle physics. The resolution of the problem has been obtained by solar neutrino experiments and the KamLAND reactor neutrino experiment. KamLAND has obtained a clear signature of oscillatory neutrino behavior and, as a result, it has determined a neutrino oscillation parameter related to neutrino mass very precisely. Now the accumulated knowledge on neutrino propagation opens new research area by using neutrinos as a prove of interior of the earth and the sun.
