To provide a financial system using IC card capable of preventing the leak of authentication data to be transmitted when providing a financial service through a communication network.

This system comprises a server, a user terminal with an IC card reader/writer, and an IC card. The IC card has a storage means storing a secret key and a digital certificate, and a coding means. The IC card reader/writer has a means for reading the digital certificate and encrypted authentication data, and a means for transmitting the authentication data to the IC card. A communication terminal has a means for transmitting the digital certificate and the encrypted authentication data to the server. The server has a database registering account information, a decoding means, a collation means for collating decoded authentication data with registered authentication data, and a control means for performing processing a financial transaction service when the collation by the collation means is successful.