1. A pattern recognition method for identifying which category of a plurality of categories an input pattern matches, the method comprising: calculating similarities of the input pattern with respect to respective categories; converting the calculated similarities of the input pattern with respect to the respective categories into first evaluation values based on a first table which indicates a relationship between similarities for respective categories and first evaluation values; calculating second evaluation values based on the calculated first evaluation values for the respective categories and prior probabilities for the respective categories stored in a second table indicating prior probabilities of the respective categories; and selecting a category corresponding to a maximum value of the calculated second evaluation values.