Generation processes of the characteristic raindrop-size spectra reported in Part 1 of this paper were investigated by numerical experiments. Intermittent supply of liquid water content with a certain size spectra was introduced in the well mixed cloud model under the action of drop breakup and coalescence, corresponding to the observation fact of combination of cell echoes by radar. The results represent well the terminal state of size distribution as observed at Hitoyoshi, which is characterized by the numerous space density of drops smaller than 1mm diameter, the high population of large drops, and the flat shape in medium size range. Furthermore, the very flat distribution which is frequently observed at the beginning stage of shower rain was obtained by the one dimensional sedimentation model in which the rain with the stationary distribution was released at the upper level. The Z-R relation derived from the above computational results may be well represented by Z=383R^<1.6> which was obtained in Part 1.