To obtain a laser diffraction-type measuring apparatus by which a uniform and thin sample layer can be formed irrespective of whether the kind of a sample to be measured is dry or liquid and by which the generation of a multiple scattering can be made extremely small even when the concentration of the sample is high.

A circular hollow (a recessed part) 2 is formed on a cell 1 which is constituted of a plane glass or the like. Regarding the depth of the hollow 2, cells whose hollow has various depths are prepared when a sample is a suspension. According to the kind of the sample, one cell is selected out of the cells in such a way that a laser beam can be transmitted. When a dry powder is used as the sample, the size of particles is estimated in advance, and the cell in which the depth of the hollow 2 is a little deeper than the diameter of a largest particle in the sample is used. When the cell 1 is constituted in this manner so as to put the sample to be measured into the hollow, a thin sample layer can be formed, and the generation of a multiple scattering operation can be made extremely small even when the concentration of the sample is high.