1. A pattern recognition apparatus comprising: an extracting section for extracting, from a query image that is composed of at least one piece of pattern component and previously undergoes a geometric transformation, the pattern component; a feature acquiring section for acquiring a geometric invariant feature of the pattern component as a query feature, the query feature being represented by at least three feature points including first, second and third feature points, each feature point locating on the pattern component and being retrieved from the pattern component based on a predetermined rule; a comparing section for comparing the query feature with a plurality of reference features, each reference feature representing different reference patterns prepared as candidates for pattern recognition; and a pattern determination section for determining, as a recognition result, a specific reference pattern out of the candidates based on a similarity of features therebetween and, wherein: each reference feature is represented using feature points retrieved from each reference pattern based on the same rule as that of the query feature, and based on the predetermined rule, a position of the first feature point is specified out of points which locate on the pattern component and are invariant to the geometric transformation, a position of the second feature point is specified using a characteristic regarding a shape of the pattern component, the characteristic being invariant to the geometric transformation, and a position of the third feature point is specified from a predetermined value being invariant to the geometric transformation and from the specified positions of the first and second feature points.