A user authentication system and method using a password. A method for performing an operation mode associated with a password in the system having a password setup function, includes the steps of setting up a general password for normal user authentication and an emergency password needed for an emergency operation mode, and storing them in a memory; and upon receiving a password from a user, performing the normal user authentication when the user-entry password matches the general password, and performing the emergency operation mode when the user-entry password matches the emergency password.