An immunoassay analyzer for determining the presence or absence of a substance to be detected in a sample by detecting color change due to a specific immunoreaction in a sample analysis tool, the immunoassay analyzer comprising: an optical detection unit for detecting color change in the sample analysis tool; and a determination unit for determining the presence or absence of the substance to be detected based on information from the optical detection unit, the optical detection unit comprising an optical signal measurement unit for measuring an optical signal at each of two or more different wavelengths including a main wavelength for detecting the color change due to the specific immunoreaction and a sub-wavelength other than the main wavelength, the determination unit comprising a discrimination unit for comparing the respective optical signals at the two or more different wavelengths, including the optical signal at the main wavelength and discriminating between the color change due to the specific immunoreaction and color change due to a cause other than the specific immunoreaction based on a comparison criterion determined previously, wherein, in the discrimination unit, the comparison criterion is a standard value for a magnitude relationship between the optical signal at the main wavelength and the optical signal at the sub-wavelength, the optical signal at the main wavelength is compared with the optical signal at the sub-wavelength based on the standard value for the magnitude relationship, and the color change due to the specific immunoreaction and the color change due to a cause other than the specific immunoreaction are discriminated based on a result of the comparison, wherein, in the determination unit, it is determined that the sample is negative regarding the substance to be detected where color change in the sample analysis tool is not detected in the case where an optical signal at the main wavelength is not detected, wherein it is further determined that the sample is negative when the optical signal at the main wavelength indicates that no color change of the sample analysis tool is detected based on a previously determined standard, and when color change in the sample analysis tool is detected, the discrimination unit discriminates whether the detected color change is due to the specific immunoreaction or a cause other than the specific immunoreaction, and it is determined that the sample is positive regarding that the substance to be detected is present in the case where the discrimination unit determines that the detected color change is due to the specific immunoreaction, and it is determined that the determination is invalid in the case where the discrimination unit determines that the detected color change is due to a cause other than the specific immunoreaction. an optical detection unit for detecting color change in the sample analysis tool; and a determination unit for determining the presence or absence of the substance to be detected based on information from the optical detection unit, the optical detection unit comprising an optical signal measurement unit for measuring an optical signal at each of two or more different wavelengths including a main wavelength for detecting the color change due to the specific immunoreaction and a sub-wavelength other than the main wavelength, the determination unit comprising a discrimination unit for comparing the respective optical signals at the two or more different wavelengths, including the optical signal at the main wavelength and discriminating between the color change due to the specific immunoreaction and color change due to a cause other than the specific immunoreaction based on a comparison criterion determined previously, wherein, in the discrimination unit, the comparison criterion is a standard value for a magnitude relationship between the optical signal at the main wavelength and the optical signal at the sub-wavelength, the optical signal at the main wavelength is compared with the optical signal at the sub-wavelength based on the standard value for the magnitude relationship, and the color change due to the specific immunoreaction and the color change due to a cause other than the specific immunoreaction are discriminated based on a result of the comparison, wherein, in the determination unit, it is determined that the sample is negative regarding the substance to be detected where color change in the sample analysis tool is not detected in the case where an optical signal at the main wavelength is not detected, wherein it is further determined that the sample is negative when the optical signal at the main wavelength indicates that no color change of the sample analysis tool is detected based on a previously determined standard, and when color change in the sample analysis tool is detected, the discrimination unit discriminates whether the detected color change is due to the specific immunoreaction or a cause other than the specific immunoreaction, and it is determined that the sample is positive regarding that the substance to be detected is present in the case where the discrimination unit determines that the detected color change is due to the specific immunoreaction, and it is determined that the determination is invalid in the case where the discrimination unit determines that the detected color change is due to a cause other than the specific immunoreaction.