To facilitate processing for settlement of accounts by reading information required for calculating an interest amount in an account out of a storage means by a central processing unit (CPU), and calculating the interest amount based on this information.

Information written on a bankbook (and/or card) Y concerning an account number (identification information) is read by a first reading means 1. A first control means 4 transmits the read information on the account number from a first communication means 3 to a CPU B. Based on the received information on the account number, a second control means 9 reads the information, which is required for calculating the interest amount, on the account out of a relevant account information file in a second storage means 6a. Then, the interest amount is calculated by a second arithmetic means 7. The second control means 9 stores the information of the calculated result and information showing the execution of interest amount calculation in the relevant account information file of the second storage means 6a. Besides, the information of the calculated result is transmitted through a second communication means 5 to terminal equipment A.