1. An identification apparatus comprising a processor executing a process that causes the identification apparatus to perform: determining two or more classes into which input biometric data is classified out of a plurality of classes based on features of the input biometric data, where a plurality of items of registered biometric data have been classified into at least one of the plurality of classes; calculating similarity between the input biometric data and each item of the registered biometric data registered in each of the determined two or more classes into which the input biometric data is classified; and identifying data on a user who has entered the input biometric data among the registered biometric data registered in any of the determined two or more classes, based on the similarity to the input biometric data; and setting a threshold for each of the determined two or more classes in order to identify data on the user who has entered the input biometric data, wherein each of the classes is set in advance, when, among the registered biometric data registered in each of the determined two or more classes, there is at least one biometric data item whose similarity to the input biometric data exceeds the threshold set for each of the determined two or more classes, the identifying identifies that the input biometric data and the registered biometric data item belong to the same user.