Content is transmitted within a range of the user's legitimate use while limiting the number of equipment to which the content is transmitted at the same time.A content using apparatus periodically transmits an exchange key and the corresponding key ID using a command. Only while receiving the key ID at predetermined reception cycles, a content providing apparatus maintains the corresponding exchange key. When not periodically receiving the key ID, the content providing apparatus destroys the corresponding exchange key. After that, when receiving a command including the key ID, the content providing apparatus returns a response including information indicating that the exchange key has become invalid.