Constitution of the Republic of China (Taiwan) Article 50
The President shall be relieved of his functions on the day on which his term of office expires. If by that time the succeeding President has not yet been elected, or if the President-elect and the Vice-President-elect have not yet assumed office, the President of the Executive Yuan shall act for the President.
中文原文 中華民國憲法第50條
總統於任滿之日解職，如屆期次任總統尚未選出，或選出後總統副總統均未就職時，由行政院院長代行總統職權。