It is an object to provide an user identity authentication system and an user identity authentication method with the Internet and a mobile information communication device. The mobile information communication device includes a liquid crystal device with a built-in image sensor. The image sensor reads individual information of a user, and user's identity is authenticated based on the individual information. A result of the authentication is unicast via the Internet. Alternatively, it is judged whether or not the result of the authentication is required to be unicast in accordance with a degree of requirement preset in the mobile information communication device or a destination terminal of communication, and the result is unicast via the Internet only when needed.