To solve a problem that if a free address system for workers is realized in a thin client system environment, tools such as authentication devices, mouse, IP phones must be prepared for the workers respectively, but the tools may be lost.

A communication system includes a thin client terminal, an input device connected to the thin client terminal, and a server connected to the thin client terminal via a network, wherein the input device has an authentication device storing user information, a mouse, and an IP phone unit connected to the mouse via a coupling unit, and the thin client terminal performs authentication processing for a connection with the server on the basis of the user information read out of the authentication device and transmits connection information between the mouse and the IP phone to the server for authentication processing of the connection.