2011 年 2011 巻 57 号 p. 21-30
For the Upper House election in 2010, the DPJ ran multiple candidates in most of the two-member districts. In this paper, we argue the mechanism of two-member districts and whether the result of, what is called, “Ozawa strategy” of the Upper House election in 2010 succeeded. Chapter 1 shows that two-party members have occupied most of the seats in the Diet since the Japanese Lower House implemented election reforms in 1994, and the effective number of candidates of two-member districts in the Upper House in 2007 was 2.99―the only number to be lower than that projected by the M+1 rule. In Chapter 2, we argue the effect of running multiple candidates in two-member districts of the Upper House and show one cost, both candidates lose of a two-member district, and two benefits, monopolization of a two-member district and the influence on nationwide proportional districts. In Chapter 3, we argue the possibility that a party runs multiple candidates. By the data of past elections in the Upper House, the possibil-ity that both candidates lose and a party monopolizes two-member districts seems to have diminished more and more since the institution of a two-party system. On the other hand, with regards to influence on nationwide pro-portional districts, a nationwide party can enjoy benefits by running multiple candidates in each two-member district. Chapter 4 shows the reason why DPJ, not LDP, take the multiple candidates strategy and why it happens in 2010 and we argue whether the result of, what is called, “Ozawa strategy” of the Upper House election in 2010 succeeded. It is said that the result of “Ozawa strategy” succeeded because the possibility of a party monopolization of a two-member district was low, DPJ, however, gained one seat in each district and the votes in a nationwide proportional district increased.