PROBLEM TO BE SOLVED: To provide a dimension measuring apparatus for a metal thin plate, capable of accurately measuring a dimension of a metal thin plate, and a dimension measuring method for a metal thin plate.SOLUTION: A dimension measuring apparatus 11 for a metal thin plate includes: a loading plate 21 on which a metal thin plate is loaded; a pair of retention mechanisms 22a, 22b configured to hold two opposite sides of the metal thin plate loaded on the loading plate 21; a tension mechanism 23 configured to widen a distance of the pair of retention mechanisms 22a, 22b to each other so as to impart a tensile strength to the metal thin plate; and a measurement mechanism 13 configured to measure at least one dimension of the metal thin plate with the tensile strength imparted.
