1. A biometric authentication device comprising: a storage unit that stores a plurality of pieces of reference biometric data; an identification control unit that extracts reference biometric data where a coefficient for determining a similarity to acquired biometric data is greater than or equal to a first threshold value; a similar region extraction unit that obtains coefficients for determining similarities between the plural pieces of extracted reference biometric data, in units of predetermined regions, and extracts a similar region where the coefficient for similarity determination is greater than or equal to a second threshold value when a plurality of pieces of reference biometric data are extracted by the identification control unit; and a judgment unit that weights a coefficient for determining a similarity to a dissimilar region, compared with the coefficient for determining a similarity to the extracted similar region, and judging the degree of similarity between the biometric data and the plural pieces of extracted reference biometric data.