PURPOSE: To enable to perform a detection of an intermediate point of filteration in conformity with the motion of a syringe, by installing a cuvette for optical photometery conforming to a photometer making a measurement of fluorescence and scattered light after verifying that suspension can be filtered by a porous filter.

CONSTITUTION: In the case of suction filteration, a tube vertical moving mechanism 8 provided with a flow path system tube 7 is first lowered, and the tube 7 is inserted into a cuvette 1 for suspension photometry. Then, a switch valve 12 closes off the flow path, and in a spindle vertical moving mechanism 11 positioned at a lower dead point, a position detector 13 detects the state by means of a detecting panel 15. If a suction filteration starts, a piston 10 in a syringe 9 is lifted in a rise direction by the piston vertical moving mechanism, and in which case, the detecting panel 15 is detached from the position detector 13 to detect starting of filteration. Suspension 2 in the cuvette for suspension photometry is introduced to a flow path tube, particles in the suspension 2 are filtered by a porous filter 3, and filterate 4 is stored in the syringe.