A spheroidal mirror reflectivity measuring apparatus for extreme ultraviolet light may include an extreme ultraviolet light source, an optical system, and a first photosensor. The extreme ultraviolet light source may be configured to output extreme ultraviolet light to a spheroidal mirror that includes a spheroidal reflection surface. The optical system may be configured to allow the extreme ultraviolet light to travel to the spheroidal reflection surface via a first focal position of the spheroidal mirror. The first photosensor may be provided at a second focal position of the spheroidal mirror, and may be configured to detect the extreme ultraviolet light that has passed through the first focal position and then has been reflected by the spheroidal reflection surface.