User authentication system

The present invention provides a user authentication system, which spares a setting input operation for user authentication prior to data communication between a portable terminal and an image forming apparatus, thus reducing the user's burden of inpu operation. The portable terminal includes a first sound output unit and a first sound input unit, and the image forming apparatus includes a second sound output unit, a second sound input unit, an authentication information generating unit generating a security code, a storage unit storing the generated security code, and an authentication confirmation unit performing a user authentication by using the security code. When the first sound input unit receives a first synthesized sound, which includes the stored security code and is outputted from the second sound output unit, the first sound output unit outputs a second synthesized sound including the security code extracted from the received first synthesized sound, and the authentication confirmation unit determines that a user authentication is successful when the stored security code and the security code extracted from the received second synthesized sound match.