1. A speech recognition device comprising: means for supplying an input speech signal; means for converting said input speech signal into an input pattern indicative of features of said input speech signal; a similarity measure calculating unit for calculating primary similarity measures between said input pattern and a first plurality of prepared reference patterns and for selecting a maximum value of said primary similarity measures as a provisional similarity measure; similarity measure calculating means for calculating secondary similarity measures between said input pattern and a second plurality of produced reference patterns produced in compliance with said prepared reference patterns and for selecting a maximum value of said secondary similarity measures as a reference similarity measure; a similarity measure correcting unit connected to said similarity measure calculating unit and said similarity measure calculating means for correcting said provisional similarity measure by modifying said provisional similarity measure by either a difference between said provisional similarity measure and said reference similarity measure or a ratio of said provisional similarity measure and said reference similarity measure and for outputting said corrected provisional similarity measure as a corrected similarity measure; and a normalizing unit connected to said similarity measure correcting unit for normalizing said corrected similarity measure into a normalized similarity measure by a duration of time of said input pattern.