1. A biometric authentication device comprising: a memory; and a processor coupled to the memory and configured to execute a process including: comparing acquired biometric data with a plurality of pieces of reference biometric data; when a match occurs between the acquired biometric data and at least two of the plurality of pieces of reference biometric data, determining whether corresponding regions in the at least two of the plurality of pieces of reference biometric data are similar to each other, the at least two of the plurality of pieces of reference biometric data being divided into regions; weighting similar regions among the corresponding regions, with a first weighting and weighting dissimilar regions of the at least two pieces of reference biometric data with a second weighting which is different from the first weighting; and judging a degree of similarity between the acquired biometric data and the weighted pieces of reference biometric data, based on the weighted similar regions and the weighted dissimilar regions.