Supernovae are the explosions that announce the death of stars. I investigate the physical processes involved under these extreme conditions, and evaluate the use of these explosions as probes of the cosmology and the evolution of the Universe. So far, I have worked primarily on supernova explosions of massive stars: nucleosynthesis and radiation processes to simulate their appearance, and observations mainly using the Subaru telescope. My research activities revealed that the explosion geometry is far from spherical, and that this is an intrinsic ingredient of the supernova explosion. Also, the deviation seems to be larger in more energetic explosions which are linked to high energy transients called gamma-ray bursts. Currently, my research is mainly on TypeＩa supernovae, which are the thermonuclear explosions of white dwarfs. The aim is to clarify the still-unknown progenitors and explosion mechanisms, to provide a solid basis for using these luminous objects in cosmological study, and then to come up with new ideas with which to explore the evolution of the Universe.