Directions for Tax System Redesign in Shrinking Societies / 人口減少社会における税制再設計の方向性

Short Abstract This paper examines how demographic decline and population aging undermine the sustainability of tax systems that rely heavily on labor- and production-based tax bases, especially personal income tax and corporate tax. It argues that modern tax regimes face compounded structural constraints: volatility of taxable income as the working-age population shrinks, tax base erosion driven by cross-border capital mobility, and rising administrative and compliance costs caused by increasing complexity. Reframing taxation as a core institutional infrastructure of the state, the paper proposes a redesign direction that shifts the fiscal center of gravity toward consumption, emphasizing a “Selective Consumption Tax” (Choice-Tax) as the primary revenue pillar. The Choice-Tax embeds tiered/selective elements into consumption taxation based on the content and level of consumption, enabling revenue stability and improved administrative efficiency. Since taxation is determined automatically at the transaction stage, the model can reduce reliance on labor-intensive processes such as filing, auditing, and investigations—an important advantage under future public-sector labor constraints. Rather than abruptly abolishing income and corporate taxes, the paper recommends a gradual, predictable transition in which these taxes are redefined as supplementary and adjustment instruments while the primary revenue role migrates toward the Choice-Tax. An appendix discusses international competitiveness, highlighting border-adjustment consistency and the benefits of institutional simplicity for investment and talent mobility. ORCID: https://orcid.org/0009-0003-1530-4234 Japanese Abstract 本論文は、人口減少・高齢化が進行する成熟社会において、現行の所得税・法人税中心の「労働・生産活動依存型」税収構造が、課税ベースの不安定化、国際的資本移動による税源浸食、税制複雑化による行政事務コスト増大といった複合的制約に直面している点を整理し、税制を国家運営の「制度インフラ」として再設計する方向性を提示する。中核提案は、課税ベースとして捕捉性と安定性に優れる「消費」に重心を移し、消費の内容・水準に応じた段階性/選択性を内包する消費課税(選択税)を主税として位置付けることで、歳入安定性と行政効率を同時に高めるという制度概念である。選択税は取引時点で課税が自動的に完結し、申告・審査・調査に依存する運用負荷を縮減し得るため、人的資源制約が強まる将来の税務行政にも適合しやすい。さらに、法人課税・所得課税を即時否定するのではなく、役割を補完的・調整的機能へ再定義しつつ段階的に比重を移行する「連続性を保った再編」を重視する。付録では、消費課税中心モデルが国境調整効果・制度単純性を通じて国際競争力と整合し得る点を補足的に論じる。