There is provided a high-accuracy automatic analysis device achieving both of measurement in a wide concentration range and high sensitivity at a low concentration. The signals of a plurality of wavelengths λ1 to λ12 where the sensitivity of light absorption caused by fine particles is high from a light source 40 are converted to absorbances by a spectroscopic optical system (detector) 41. The absorbances are converted to a secondary parameter from in which a noise component is cancelled by using a previously-defined conversion table 54, so that a concentration of a measured material (predetermined component) is calculated by an operation unit (calculating means) 53 based on the secondary parameter. Thus, analysis being resistant to the noise even at the low concentration can be achieved in a range up to a high concentration.