There is a model of the climatic productivity of paddy rice which has been introduced by the author and Hanyu. The model has been named the "climatic productivity index of paddy rice", and it might be used as the index of climatic productivity which gives potential productivity of paddy rice under given climatic conditions. In this paper the limit value of the index expressing the climatic productivity at the limit of its cultivation was investigated. Judging from both sides of northern limit and height limit, it seemed that the limit value of its cultivation, Y_＜po＞ = 500 was reasonable as far as the normal climate. In individual years, we could expect for more or less harvests (about 200kg/10a) at Y_＜po＞ = 500, assuming good cultivation conditions. In the years of cool summer damage the distribution of the index and the unit yield were illustrated, and in the regions less than the limit value, a great deal of damage including completely ruined harvests are anticipated. Finally, the movement of the limit line in the case of climatic variations was investigated.