PURPOSE: To measure the rates of reaction in reaction tubes quickly and accurately despite the difference in the absorption sensitivities and calibration curves of photometric devices in plural measuring parts by providing two calibration plates into a reaction line which moves cyclically.

CONSTITUTION: A reaction line is driven cyclically by a driving device. When calibration plates 3b, 3a pass through measuring parts 6a, 6b successively, rays are emitted from projectors 4a, 4b and the rays transmitted through the plates 3b, 3a are stored in an arithmetic part 9 via photometric devices 5a, 5b, amplifiers 7a, 7b, and A/D converters 8a, 8b. In accordance with these signals, the part 9 calculates the correction equation of making the calibration curve B with respect to the part 5b coincident with the calibration curve A with respect to the part 5a and stores this. Next, a reaction tube 1 is located in the measuring parts 6a, 6b, and the quantity of the light transmitted therethrough is measured. The concn. of enzyme is determined by the calibration curve and from the change in the absorbancy obtd. by this, the rate of reaction is calculated. Thereby, the need for checking absorption sensitivities and calibration curves at the start of the use is eliminated.