1. A pattern classification method comprising: extracting a quantity of pattern characteristics from a pattern classification target; registering and setting classification category information corresponding to said quantity of pattern characteristics in a pattern dictionary; and performing pattern classification based on said quantity of pattern characteristics and a Mahalanobis dictionary registered in said pattern dictionary, wherein said Mahalanobis dictionary is created by performing optimization processing of said pattern dictionary based on said classification name and said quantity of pattern characteristics stored in said pattern dictionary.