Disclosed is a password authentication system and a password authentication method using continuous password authentication. In the password authentication system, a password is set using an original password and a shift value, and the password authentication system includes a password authentication unit configured to receive a password subjected to the shift value, apply the shift value inversely to the password to obtain the original password and perform authentication processing, a defense mode changing unit configured to change to a defense mode requiring continuous authentication of the password at least twice, and a defense mode control unit configured to require the user to continuously input a first password and a second password, and to determine the authentication of the password as a success and release the defense mode.
