The present invention relates to an improved abnormality determining method for an automatic analyzer and related automatic analyzer that detects abnormalities for a reaction process of a reaction solution. The method for determining the presence of absence of abnormalities in the reaction process and performs the determination by acquiring acquisition conditions for multiple items of measured data, acquiring the measured data detected by a spectral detector that match the acquisition conditions, calculating a feature quantity of the measured data, generating a determination criterion based on the feature quantity, and determining the presence or absence of abnormalities by comparing the feature quantity of the measured data subject to the determination with the determination criterion. The acquisition condition includes information relating to a number of a divisions of a measured value range and information relating to the number of items of data in each divided segment.