PURPOSE: To accurately grasp minute luminous points distributed in a particle three-dimensionally accurately, and to accomplish an accurate counting, by photographing plural different luminous images to a single particle.

CONSTITUTION: By leading in a sample solution 2 a fluorescent mark is applied to a flow cell 1, the cells (particles) of the sample flow included in a sheath solution flow by lining up in one line, and when they are in the photographing area in the flow cell 1, a light source 3 is excited. And an excited single cell is photographed from two different directions. That is, a fluorescent image passing through a lens 4, and obtained by object lenses 5 and 6 are reflected by mirrors 7 and 8 respectively, they are reflected again 9, and the images are formed on the photoelectric screen of an image intensifier (I. I) 12. The I, I 12 amplifies the two faint fluorescent image in several ten thousand times, and they are photographed by a video camera 10. An image processor 11 inputting the resultant video signal carries out the counting of the number of fluorescent luminous points, the calculation of the fluorescent luminous amount, and the like. Consequently, the luminous points distributed in the cell three- dimensionally can be discriminated, and the luminous points can be counted accurately.