Lawmakers on Friday enacted a bill to revise the national referendum law to reduce its minimum voting age to 18 from 20.
The bill, approved by a majority vote at the House of Councilors amid Prime Minister Shinzo Abe's push to alter the Constitution to get around war-renouncing Article 9, is designed to lower the minimum voting age for national referendums four years after the revision takes effect.
The Liberal Democratic Party, its ruling coalition partner, buddhist-backed New Komeito, and the main opposition Democratic Party of Japan were among the parties voting in favor of changing rules under the law concerning procedures for amending the Constitution.
The Japanese Communist Party and the Social Democratic Party voted against it. The Lower House approved it May 9.
A proposal for revising the Constitution can be initiated with the support of at least two-thirds of the lawmakers in both houses of the Diet and must be endorsed by a majority in a referendum.
The issue of amending the Constitution, which has never been revised since its promulgation in 1946, remains a source of conflict between parties, largely due to Abe's stance and his nationalist reputation.
The prime minister has expressed his desire to revise the charter, partly to bolster the nation's defensive capabilities.
He is attempting to permit the Self-Defense Forces to come to the defense of allies under armed attack by legalizing use of the so-called right to collective self-defense, which is banned under the government's interpretation of the pacifist Constitution.
While supported by some countries, including the United States, Abe's bid to get Japan more proactively involved in international operations to ensure peace and stability have aroused the concerns of Asian neighbors such as China and South Korea, which suffered from Japan's wartime aggression.