the u201c pattern u201d refers to physical information capable of specifying a category which includes face image fingerprints voice characters and dna the input subspace generating unit 102 when feature vectors are acquired in a predefined number generates an input subspace based on principal component analysis the reference subspace storing unit 103 stores in the number r of reference subspaces which are generated by the principal component analysis 4 subspace projecting units 105 1 105 m each of the subspace projecting units 105 projects the input subspace and reference subspaces stored in the reference subspace storing unit 103 onto one of the constraint subspaces stored in the constraint subspace storing unit 104 the procedure of projection is detailed in jp a 2000 30065 and maeda et al cited on p 2 5 similarity calculating units 106 1 106 m each of the similarity calculating unit 106 calculates similarities between the reference subspaces and the input subspace in a state having been projected onto one of the constraint subspaces by the mutual subspace method the similarity combining unit 107 takes an average value maximum value minimum value or median value from a plurality of similarities obtained by using constraint subspaces hereinafter referred to as a combined similarity in this description calculating an average etc of similarities for each reference subspace is referred to as u201c combining u201d when the combining is made by taking the average value a similarity s e is determined by equation 6 s e 1 m u2062 u2211 1 u2264 i u2264 m u2062 cos 2 u2062 u03b8 c i 6 where m represents the number of constraint subspaces and u03b8 ci represents an angle between p ci and q ci which are the subspace p.