Japanese Politics Central has results from 1946 onwards. These include seats, national level and district level. It also links to Japanese sources of election results.
The Comparative National Elections Project (CNEP) currently includes 24 national election surveys conducted in 19 countries since 1990. It is based at the Social Sciences Institute of the University of Lisbon. The 3 phases of research share a common concern with the processes of intermediation through which citizens receive information about policies, parties, candidates, and politics in general during the course of election campaigns. It includes data taken from Japan in 1993
The Japanese Data Archive us based at the Roper Center for Public Opinion Research. It provides access to a large collection of materials relating to Japanese public opinion poll research. It includes free access to JPOLL an online question level database of Japanese material. This contains over 10,000 questions and responses from Japan's major social, cultural and political attitude surveys conducted in the last decade. Free registration is required. All materials are translated into English. The site also holds a searchable catalogue of datasets. It provides references to over 1,500 research reports and 200 series from 1980 onwards, with some party identification data available from 1946 onwards.
A User's Guide to Past Japanese Election Studies (English language)
Part of the Virtual Library on Democracy created by The Center for the Study of Democracy at the University of California, Irvine, this provides an annotated list of major election surveys and information on where data may be obtained. Most are not in ful text online but it indicates where they may be found.
For Japanese language readers! The Association for Promoting Fair Elections
Includes data on voter turnout rate changes on national and local levels from 1946 on and public opinion polls from all postwar elections.
Asian election Studies is another good site.It includes news, conference alerts and links to studies and statistics on elections in a number of Asian nations.