An identifier management apparatus capable of setting identifier conversion information of a new user without affecting identifier conversion processings of other users, and an identifier management method. The identifier management apparatus converts an identifier given to communication data. Its memory stores multiple hash functions, output values of the hash functions corresponding to the respective plurality of hash functions, multiple entry tables that manage the identifier conversion information indicating a correspondence between the input identifier being an input value of the hash function and an output identifier obtained by converting the input identifier, and a management table for managing a setting status of the identifier conversion information in each entry table. When registering the new identifier conversion information in any entry table, its processor selects an entry table that should register new identifier conversion information depending on setting statuses of the identifier conversion information in the entry tables.