User authentication method using password

A user authentication method includes the steps of: inputting, by a user, a predetermined password having a plurality of digits; examining whether an input password includes an actual password that is predetermined by using less digits than the input password; authenticating the input password if the input password includes the actual password; and refusing to authenticate the input password if the input password does not include the actual password. The user authentication method using the password is very useful for reinforcing the security by applying a simple processing, not necessarily consuming high costs and much time. Further, even when the password may be exposed to others, it is still safe. Also, although a password may be used in many cases in common, the security still can be reinforced by differentiating the input password. Most of all, the user can remember the actual password very easily, and yet get the same effect with changing the password.