What can we learn with neutrinos?

2012 is the 25th year from the observation of SN1987A with which the neutrino astronomy was born. Our understanding of neutrinos has been drastically changed in the last 25 years. The discovery of neutrino oscillations by atmospheric neutrinos showed that neutrinos have masses, and the solar neutrino problem was solved by neutrino oscillations. Accelerator and reactor neutrino experiments were also performed. For the astrophysics probed by neutrinos, the SN1987A signals confirmed the basic scenario of the supernova explosion and the prediction of solar neutrino fluxes agree with model prediction once we correct for the effect of neutrino oscillations. The origin of cosmic rays can also be investigated by search for high energy cosmic neutrinos. The IceCube neutrino observatory has been in its full operation since 2011 and we began constraining some models of cosmic ray production mechanisms. (author)