Abstract：bservations of solar neutrinos and supernova neutrinos in Hyper-Kamiokande (HK) are discussed. The current solar neutrino observation in Super-Kamioande(SK) shows a tension in Delta m^2_{12} between solar and reactor neutrino measurements. It might indicate hint of some new physics. Quite high statistics of solar neutrino events in HK enable us to discussed the difference with high statistical significance in future by comparing HK results with the JUNO reactor measurement. JUNO and SK-Gd (gadolinium-loaded phase of SK) would discover supernova relic neutrinos (SRN). However, they would not have enough statistics to discuss spectrum of SRN. HK should be able to measure shape of energy spectrum down to 10 MeV and it would reveal supernova history in the universe back to red-shift (z) of one. If a galactic supernova occurs, large number of events are expected at HK. We can discuss evolution of explosion with time variation of event rate and neutrino temperature. In addition, HK might be able to detect dozens neutrino events from nearby galaxies upto several mega parsec.