PURPOSE: To shorten the response processing time to a terminal by adding the data if stored in a file of a decentralized computer into a response message against the response given from a host computer.

CONSTITUTION: A decentralized computer 2 holds some of the data on a host computer 1, and the presence or absence of data on the computer 2 is decided to the inquiry processing of a terminal 3 based on a data possession deciding program. This decision information is set into a message 12 and sent to the computer 1. Then the computer 1 decides whether the computer 2 possesses the data or not when the computer 1 produces a message 13 which is sent to the computer 2. Thus the computer 1 produces the message 13 except the data possessed by the computer 2 and sends the message 13 to the computer 2. The computer 2 retrieves a data file 5 distributed previously to the message 13 and adds the data stored in the file 5 to the message 13 to send a complete message to the terminal 3. As a result, the response processing time is shortened to the terminal 3.