To evaluate the temporal variation of seismicity in the Inner Zone of Southwest Japan before and after the Nankai trough events, we introduced a statistical model and estimated the value of the model parameters. We used the data of disastrous earthquakes to estimate them. Because of the lack of spatially sufficient data, we used data from the 9th century in the case of the northern Kinki region, and in the case of the whole Inner Zone of Southwest Japan only data after the 17th century. The results show that for the northern Kinki region the seismicity has a peak before the Nankai trough events, although there is no significant change before them in the whole Inner Zone of Southwest Japan. The seismicity in the Inner Zone of Southwest Japan increases just after the Nankai trough events. We compared the obtained intensity functions with the recent JMA data from 1885 to 1995. The seismicity seems to have increased in the last 30 years. Using data from this period, we estimated the occurrence time of the next Nankai trough event. Our results show that it will occur in the 2030'S.