Three hailstorms in Kanto-plane, Japan (15July 1996, 24 May 2000, 11 May 2001) are analyzed with various kinds of data including C-band Doppler radar data, aerological data and AMeDAS (Mesonet-like System) data. Environmental conditions such as CAPE, vertical wind shear and surface mesoscale analysis showed intimate relation with the scale and strength of the storm. Each storm accompanied downbursts. Microstructure of the downburst by the Doppler radar data reveals that they have complicated substructure. Precursor signal of downburst is analyzed using Doppler radar data. Three-dimensional structure of precipitation core is also analyzed by using Vis5D software.