an input unit configured to input at least one input pattern;

an input subspace generating unit configured to generate an input subspace by generating an input vector from said input pattern and analyzing a main component for said input vector;

a reference subspace calculating unit configured to calculate a reference subspace, respectively, by analyzing a main component for a reference pattern relevant to a plurality of comparison targets to compare them with said recognition target;

a constraint subspace storing unit configured to obtain a subspace for learning obtained by a main component analysis from a pattern including a variation resulting in declining pattern recognition performance and storing a plurality of constraint subspaces obtained from said subspace for learning;

a projecting unit configured to project said input subspace and said plurality of reference subspaces onto each one of said plurality of constraint subspaces;

a similarity calculating unit configured to calculate similarities between said input subspace in the projected constraint subspaces and all of said plurality of reference subspaces, individually;

a similarity combining unit configured to combine the similarities of said plurality of constraint spaces for each reference subspace and calculating a combined similarity for each reference subspace; and

a determining unit configured to determine a comparison target of the reference subspace corresponding to a combined similarity having a high value among said combined similarities as said recognition target.