A bead disposition is imaged while performing illumination by reflection illumination or penetration illumination so that a peak point of brightness brighter than the outside of a bead is observed in the inside of the bead and the circumferential portion of the bead is darker than the outside of the bead. A peak point of brightness in the inside of a bead is detected from the image data and adjacent pixels are successively painted with the peak point of brightness as a starting point, wherein the adjacent pixels have a brightness level of t2 or greater. Then, the image data is binarized. A space filling percentage of beads is calculated from the number of white or black pixels of an obtained binary image. Alternatively, binarization can also be performed after detecting a circle or circular arc pattern corresponding to a dark portion in the circumferential portion of bead from the image data by a pattern matching method and painting the inside of the circle or circular arc. In this way, the status of bead filling in a translucent screen using micro glass beads is measured.