I study core-collapse supernovae (CCSNe), which is the energetic explosion at the end of massive star's lives. I especially focus on the role of neutrino in CCSNe. I am working on the Boltzmann neutrino transport simulation, which directly solves the neutrino distribution function in phase space. Recently, I am also interested in the collective neutrino oscillation inside CCSNe, which is induced by the neutrino self-interaction.