概要

　本稿では，被選挙権年齢（法定立候補年齢）をめぐる日本の有権者の意識調査の結果を報告する．新聞社等による過去の世論調査では，人々は年齢引下げに消極的だという結果が報告されてきたが，本当にそうなのだろうか．本研究では，衆議院，参議院，市区町村議会という3 つの議会について，被選挙権年齢の引下げの賛否を質問した．また，サーベイ実験の方法を用いて，追加の関連情報（引下げを推奨する理由になりうる3 種類の関連知識）の教示により，人々の意見にどのような違いが生じるかを分析した．主な知見として，①いずれの議会についても，年齢引下げに賛成方向の回答者が過半数を超えた．②特に参議院については，年齢引下げへの賛成割合が高く，賛成方向の回答者が8 割弱を占めた．③特に若者回答者（18 歳から29 歳まで）は，いずれの議会についても，年齢引下げに賛成する傾向が強かった．④関連情報の教示によって，被選挙権年齢への賛成傾向が強まることが確認され，特定の層の人々への特徴的な効果もいくつか見受けられた．

Abstract

Previous opinion polls conducted by newspapers in Japan have suggested that the public is generally unsupportive of lowering the age of candidacy (the minimum legal age for eligibility to run for election). But is it truly the case? This article reports the results of an original survey experiment exploring Japanese citizens’ attitudes toward the candidacy age. Respondents were asked whether they supported or opposed lowering the candidacy age for three legislative bodies: the House of Representatives, the House of Councillors, and municipal councils. Using a survey experiment method, this study also investigates how the provision of supportive information influences public attitudes on this issue. In contrast to a control group, which received no additional information, three treatment groups were presented with different types of supportive information (e.g., the situation of candidacy ages in other countries). The key findings: (1) For all three types of legislative bodies, a majority of respondents supported lowering the candidacy age. (2) Support was particularly high for the House of Councillors, with nearly 80% of respondents in favor. (3) Youth respondents (aged 18–29) were more likely to support lowering the candidacy age. (4) The provision of supportive information significantly increased support for lowering the candidacy age, with some notable effects observed among specific demographic groups.