Japan follows the parliamentary system in accordance with the constitution of 1947. The most significant change from the previous constitution of 1889 was the transfer of sovereign power from the emperor to the people. The emperor is now defined as "the symbol of the state and of the unity of the people." The constitution provides for the supremacy of the National Diet as the legislative branch of the government, upholds the separation of legislative, executive, and judicial powers, and guarantees civil liberties.
The executive branch is headed by a prime minister selected from the Diet by its membership. The cabinet consists of the prime minister and 17 state ministers (as of February 2003), each heading a government ministry or agency. At least half the ministers must be selected from the Diet, to which the cabinet is collectively responsible. Upon a vote of no confidence by the house of representatives, the cabinet must resign en masse.
The National Diet is bicameral. The house of representatives (the lower house) has a membership of 480, with terms of office for four years, except that all terms end upon dissolution of the house (a law promulgated in February 2000 reduced the composition of the House from 500 to 480 members). From 1947 through 1993, Representatives were elected from 130 "medium" (multiple-member) constituencies, apportioned on the basis of population. The house of councilors (the upper house) has 247 members, 121 of whom are elected from a national constituency on the basis of proportional representation, the remainder from 47 prefectural constituencies. The term of office is six years, with one-half elected every three years. The lower house holds primary power. In case of disagreement between the two houses, or if the upper house fails to take action within 60 days of receipt of legislation from the lower house, a bill becomes law if passed again by a two-thirds majority of the lower house.
Suffrage is universal, the voting age being 20 years, with a three-month residence requirement. The 1947 constitution granted suffrage to women. In January 1994, the Diet passed an electoral reform bill. In addition to new laws on campaign financing, the legislation abolished the multiple-member districts and replaced them with 300 single-member districts and 200 multimember districts. Currently, the number of multimember districts stands at 180. The 1996 elections resulted in the weakening of minor parties, in particular the SDPJ and Sakigake. Elections for the house of representatives took place in 2000 and those for the house of councilors in 2001.