PURPOSE: To update customer information of decentralized data bases according to the decentralized computer utilization state of customers.

CONSTITUTION: When a customer number is inputted from the terminal 7 of a decentralized computer 2, whether or not the customer information corresponding to the customer number is registered in the decentralized data base 10 is retrieved and when the customer information is not registered, a count table 11 accumulates the frequency of utilization by the customer number. When the accumulated value reaches a previously set numeral, the customer information is deleted from the decentralized customer data base 10 where the customer information of the customer number is registered and the customer information in the customer master data base 5 of a host computer 1 where the customer information is registered altogether, is sent from a communication control unit 5 to the communication control unit 2 of the decentralized computer 2 where the accumulated value reaches the set value and registered in the decentralized customer data base 10.