To simplify input work and to increase a ratio of the display of customer information in retrieval by a telephone number.

When a telephone call is received through a line, the telephone number is received, a customer telephone number retrieval function 31 retrieves a customer telephone number file 35 with the telephone number as a key and displays customer information. However, when the corresponding customer telephone number file can not be retrieved, retrieval is performed with a customer name, the customer information (customer code, customer name, address, telephone number, etc.), is displayed on a screen from a customer information file 36, and the received telephone number of the caller and the displayed customer code are registered in the customer telephone number file 35.