To provide a light diffusing plate having high transmittance for light and excellent light diffusing property and to provide such a light diffusing plate of a transmission-type document reading unit in an image processing device that uniform diffused and transmitted light can be obtd. even in a small region without irregularity in the transmitted light.

This light diffusing plate is produced by compounding 0.5 to 15 pts.wt. of light-diffusing inorg. fine particles having 2 to 15μm average particle size to 100 pts.wt. of an aromatic polycarbonate resin. This plate is produced to have dark granules by ≤20 particles/cm2 and ≥40 % transmittance for all rays and ≥10 dispersion degree.