To provide a system that can dispense with an actively voluntary or conscious 'write-in' by an information provider and enables the sharing of information between constituting members and there is no problem for security.

In this so-called peer-to-peer type information retrieval system for exchanging messages between a plurality of information terminal devices in equal relation, the information terminal devices are provided with, to solve the problems, an electronic sign means to add an electronic sign by a sign key natural to the information terminal to all the messages to be exchanged, and an IC card reader/writer is provided on each information terminal device so that only a user who has an authentication card registered in advance can use the information terminal device.