Abstract: Particles in a glass substrate are measured by executing following steps: sequentially conveying a plurality of glass substrates; scanning with a camera a unit area of a glass substrate in a direction of a travel path of the glass substrate and storing particle information thereof; shifting the camera to a position corresponding to a next unit area for a succeeding glass substrate; storing information on the particles in the unit area of the succeeding glass substrate obtained by scanning the glass substrate; estimating whether a sum of the respective scanned unit areas is within an allowed limit of an area of a glass substrate; and returning to the third step if an answer from the fifth step is “No” or storing information on the particles in the entire glass substrate if the answer is “Yes”.