1. A pattern determination device, comprising: a probability computation section that computes an internal probability that is a probability in which a value of a predetermined component of a pattern that takes place according to a probability density distribution in a domain of an input pattern falls in a range between the value of said predetermined component of a pattern X (1) and the value of said predetermined component of a pattern x (2); and a dissimilarity decision section that decides a dissimilarity between said pattern X (1) and said pattern X (2) based on said internal probability computed by said probability computation means section.