1. A customer service system for use in an IC card system comprising: a customer's IC card including at least an IC circuit having first memory means for storing the personal identification number of a customer, second memory means for storing secret data, interface means for controlling the output of data from said IC card and input of data to said IC card, comparator means for comparing data input through said interface means with data stored in first memory means, and control means for controlling said first and second memory means, said interface means and comparator means in accordance with selective execution of a plurality of predetermined items of a customer service menu; display means; display control means for causing said display means to display the items of the customer service menu and to display necessary data including messages, once or repeatedly, in accordance with selective execution of said items of menu; and customer's IC card read-write means including a loading section for loading said customer's IC card, a key input section for inputting data necessary to select one of said items of the customer service menu displayed on said display means under the control of said display control means and to exchange data between said customer's IC card read-write means and said customer's IC card loaded in said loading section, an interface section for controlling the output of data to said customer's IC card or to said display control means, and the input of data from the customer's IC card or from key input section, and a control section for controlling said loading section, key input section and interface section in accordance with the selective execution of said items of the customer service menu; whereby said customer service system provides predetermined services in addition to ordinary transaction services to the customer, by permitting an access to said first and second memory means in accordance with one of the selected items of the customer service menu when said comparator means produces a coincidence output.