本文以1945年至2019年世界各民主國家的實際經驗爲觀察對 象，探討不同總統選制（相對多數制、兩輪決選制第一輪、兩輪決選 制第二輪）與憲政體制（總統制與半總統制）對於總統選舉投票率的 影響，並探討不同憲政體制與總統選制組合下總統選舉投票率的差 異，得到以下的研究發現：首先，就總統選制而言，在相對多數制下， 總統選舉投票率最高；在兩輪決選制第一輪選舉下，投票率次之；在 兩輪決選制第二輪選舉下，投票率最低。其次，就憲政體制而言，理 論上在總統制下，總統選舉投票率較高；在半總統制下，投票率較低， 但本研究在模型中卻無此發現，也顯示了總統選制對總統選舉投票率 的影響大於憲政體制。第三，就總統選制與憲政體制的組合而言，若 就總統制與半總統制國家分別觀察，在這兩種憲政體制下皆可明顯看 到相對多數制下投票率最高、兩輪決選制第一輪選舉下投票率次之、 兩輪決選制第二輪選舉下投票率最低的現象。

Based on the experiences of various democratic countries from 1945 to 2019, this study investigates the effects of different presidential electoral systems (the plurality system and the first and second rounds of the runoff system) and constitutional systems (presidential and semi-presidential systems), respectively, on voter turnout in presidential elections. Furthermore, it explores the differences in voter turnout under different combinations of constitutional and presidential electoral systems. The research findings are as follows. First, regarding presidential electoral systems, voter turnout is the highest under the plurality system, the second highest in the first round of the runoff system, and the lowest in the second round of the runoff system. Second, regarding constitutional systems, although in theory voter turnout is higher under the presidential system and lower under the semi-presidential system, this pattern is not found in our research model. This result suggests that presidential electoral systems have a more significant effect than constitutional systems on voter turnout. Third, regarding the combination of presidential electoral and constitutional systems, by observing the presidential and semi-presidential countries separately, it is evident that voter turnout is the highest under the plurality system, the second highest in the first round of the runoff system, and the lowest in the second round of the runoff system under both of the constitutional systems.