A particle size distribution analyzer is equipped with cells, a light source, to irradiate particles in a cell and multiple photo-detectors that detect a light intensity of a diffraction light and/or a scattering light generated from the particles. An information processor calculates particle size distribution based upon light intensity signals transmitted from each of the photo-detectors. A movement retention unit moves the cells between a light irradiation position and withdrawal positions. A stop unit can stop one of the cells at the light irradiation position. A cell identification unit identifies a cell situated at the light irradiation position and transmits an identification signal of the cell to the information processor, which is equipped with a program switch unit that automatically switches to an appropriate program for controlling the operation of the analyzer corresponding to the cell identification signal.