1. A method of determining an agglutination pattern type for a pattern formed in a reaction vessel, comprising: (A) setting a plurality of reference spaces based on one or a plurality of types of typical reaction images; (B) setting one or a plurality of types of unit regions in each of the reference spaces obtained in (A) and determining a Mahalanobis distance for each unit region, wherein the one or a plurality of types of unit regions comprise a first unit region, the first unit region includes a collected portion at which particles are most concentrated area and a reaction image portion other than the collected portion, wherein the collected portion and the reaction image portion other than the collected portion are in the same typical reaction image of a typical agglutination image or a typical nonagglutination image; (C) setting a threshold value from each of the Mahalanobis distances obtained in (B); (D) setting one or a plurality of unit regions for a reaction image to be determined as an object image and determining the Mahalanobis distance for each of the unit regions; and (E) determining the agglutination pattern type for the object image by comparing the threshold value set in (C) with the distances determined in (D).