To prevent a malfunction by making clear the difference in detection output between a cases where a cuvette exists and a case where it does not exist between a light source and a photodetector to easily set a threshold.

When no cuvette 34 exists between an LED 48 and a photodiode 50, the light of the LED 48 is detected by the phototdiode 50, and the cuvette is supplied from a cuvette accommodation part 40. When the cuvette 34 arranged at a guide rail 44 stops at the position between LED 48 and the photodiode 50, the light to be emitted from the LED 48 to the side of the photodiode 50 is shielded by an embossing 34c of the cuvette 34 and the light of the LED 48 is not detected by the photodiode 50, or decreases to a specific threshold level or lower, thus the supply of the cuvette from the cuvette accommodation part 40 is stopped corresponding to the change of the detection signal.