An apparatus for measuring transmissivity of a patterned glass substrate. A beam radiator radiates a laser beam. A collimation lens collimates the laser beam radiated from the laser beam radiator. A beam expander expands a size of the laser beam collimated by the collimation lens. A detector has a light-receiving section, which receives the laser beam that has passed through the patterned glass substrate after having been expanded by the beam expander. A measuring instrument measures a transmissivity of the patterned glass substrate using the laser beam received by the detector.