1. A pattern features extracting apparatus comprising: a plurality of mask memories for storing a plurality of different mask pattern data whose values are obtained from Hermite's polynomials weighted by a Gaussian function; an input pattern memory for storing unknown input pattern data; means for accessing data in a predetermined area of said input pattern memory including a given position of the unknown input pattern; and means for convolving the data accessed corresponding to the unknown input pattern data using the plurality of different mask pattern data in said plurality of mask memories.