To make it possible to listen to contents usable on a user terminal on another user terminal on trial without any trouble.

When each portable terminal transmits a demand for contents information including a user ID, a delivery server delivers streaming data of contents usable by the user. When the portable terminal allows another portable terminal to listen to the contents on trial, trial listening permission information including the own user ID and the contents ID of applicable contents and attached with an electronic signature is transmitted. After the certification, the delivery server-delivers streaming data of the trial-listening contents with the contents ID and the user ID as a retrieval key.