Supernova neutrinos, direct messengers of the core-collapse event, have been studied by many researchers.  Diffuse neutrino background from 
cosmological supernovae is considered to be realistically detectable in the near future.  I review recent progress of theoretical and 
observational studies about this topic, and discuss prospects of future large volume detector era.

I also introduce another (more recent) project, i.e. predicting the detectability of supernova neutrinos from nearby (~3 Mpc) galaxies, using 
the future megaton detectors.  Detection of these neutrinos would provide rich information, most importantly for gravitational wave searches.