Abstract: To prevent a preview of contents by a person who does not have a right to view or listen, by distributing encoded contents data which are difficult for a third person to decode. A new participation terminal apparatus, as well as transmitting a participation request to a parent terminal apparatus of a connection destination candidate, transmits a participation disclosure key for encoding a contents decoding key. The parent terminal of the connection destination candidate which receives the participation disclosure key from the new participation terminal apparatus generates an encoded decoding key, which is a contents decoding key encoded using the participation disclosure key received, and transmits it to the new participation terminal apparatus. The new participation terminal apparatus decodes the encoded decoding key received, using a participation secret key stored in a participation key storage section, acquiring a contents decoding key.