1. A face recognition apparatus comprising: a database that stores face information mapped to users; a face recognition unit comprising a program running on a central processing unit (CPU) configured to recognize the face information of the users; and a facial feature processor configured to calculate a similarity value of the face information between the users, and classify the users into a same group of at least two groups when the calculated similarity value is under a preset value or classify the users into different groups of the at least two groups when the calculated similarity value is above the preset value, wherein the facial feature processor is further configured to register a new user in the database, the facial feature processor being configured to calculate similarity values between face information of the new user obtained by the face recognition unit and the face information of the users stored in the database in each of the groups, respectively, select maximum values of the calculated similarity values between the new user and the users for each of the groups, respectively, and register the new user in a group having a smallest value among the selected maximum values of the similarity values.