In order to improve accuracy of determination of a blood coagulation time without requiring complicated work, a measurement unit 2 of a blood coagulation analyzer 1 irradiates a measurement specimen prepared by mixing a blood specimen and a reagent together, with lights of a plurality of wavelengths including light of a wavelength λ1 and light of a wavelength λ2, obtains information regarding an amount of transmitted light that transmits through the measurement specimen, and transmits the obtained information to a control device 4. The control device 4 calculates a blood coagulation time of the blood specimen based on information regarding a transmitted light amount based on light of the wavelength λ1. Moreover, the control device 4 determines whether a blood coagulation time can be appropriately obtained through the measurement, based on information regarding transmitted light amounts based on light of wavelength λ1 and light of wavelength λ2.

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