In this study, the climate variation from the 12th century to the 16th century in the Japanese Islands is analyzed. As proxy data of the climate variation, annual rings and the records of cherry-blossom parties, Omiwatari and climate disasters are used. On the basis of these data, the climate variation is reconstructed in detail, and the relation between the climate variation and the social variation is examined. The main result is as follows: 1) The climate variations of the several decade cycle also prevailed during this period. 2) Especially, from the end of the 15th century to the beginning of the 16th century, there was a remarkable climate variation with much cooling around the winter. 3) During the cooling period, famines and riots occurred frequently and the more unstable social situation was brought about. 4) Through this period, the climate was warm till the first half of the 12th century, became low after the 13th century, and cooled down after the second half of the 15th century.