TOKYO - Natsuo Yamaguchi, leader of Japan's ruling coalition party Komeito, said on Tuesday that he would step down and not run in the party's upcoming leadership election.

Stressing a smooth generational shift within the party, Yamaguchi made the announcement at a press conference during the day, marking the first leadership change for Komeito in 15 years.

The 72-year-old politician will step down upon the expiration of his eighth term on Sept 28 following his decision not to run for the leadership election scheduled on Sept 18.

Yamaguchi, who has led Komeito since 2009, has played a significant role in the coalition government with the ruling Liberal Democratic Party, notably contributing to the party's successes in national elections.

With Yamaguchi's departure, Secretary-General Keiichi Ishii, 66, is expected to run unopposed and likely to be formally approved as the new leader at the party's convention on Sept 28.