This paper ─ Litigation for Legislator Electoral District Delimitation about one man ─ one vote rule ─ Comparison between Taiwan and Japan proceeds as follow. Election is the most direct action that reflects and realizes sovereignty and human dignity, and thus institutionally protected by the Constitution. Article 129 of the Constitution indicated “one man – one vote” and article 16 of the Constitution stated “ubi jus ibi remedium (where there is a right, there must be a remedy)”. Therefore, when there is a gap in the value of votes in the electoral system and apportionment, people must have remedies. However, the Single Electoral Constituency with Two Votes System for legislator election is adopted in both Taiwan and Japan, and there is no legal basis for the electors to request a review for the apportionment of electoral district. To remedy this legal loophole, from 1976, Supreme Court in Japan steadily made an extension to the lawsuit of invalid election by examining the constitutionality of the provisions of the Public Offices Election Act 204 on election campaigns for an election. The two standards, “whether or not campaigns violate Article 14, paragraph (1) and other provisions of the Constitution” and “no correction has been made within a reasonable period of time as required by the Constitution”, and “according to the general fundamental principle of law prescribed in Article 31, paragraph (1) of the Administrative Case Litigation Act, the judgment in prior instance dismissed all of the claims of the plaintiffs, while declaring in the main text that the Election in the relevant constituencies was illegal”. In Taiwan, under the current legal system, election events can be prosecuted according to Public Official Election and Removal Law or the Administrative Procedure Law. However, from the nature of the incident and the types of litigation, it is most appropriate for the people to file an election invalidation lawsuit to dispute the uneven distribution of the number of legislators. This is similar to judicial opinion and coincides with Japanese law. In order to protect the right of election and the separation of powers, when we examine the electoral system and apportionment, in addition to examining campaigns violating the Constitution, legislative inaction must be another important standard. The purpose of the lawsuit against the division of the legislative electoral district is to conduct judicial review; whereas the purpose of the election invalidation lawsuit is to correct the flaws of election affairs by the election commissions. The two purposes are different, and the elements and the contents of judgments are also different. Therefore, it is most appropriate to formally regulate and legislate the lawsuit against the division of the legislative electoral district. As where to categorize the lawsuit, due to the particularity of the dispute, besides choosing between election litigation and administrative litigation, additional provisions in Section 4 in Chapter 3 of the Election Act may be a proper option.