The present invention is intended to provide network delivery data transmitting methods and receiving methods which allow the selection of content data as desired by user. In a data transmitting system, a specification information packet for specifying a content source used, plural packet sequences each attached with identification information, and a correspondence information packet for relating the content sources with the identification information are multiplexed with on on-air stream, which is transmitted to each receiving system via a network. On the basis of the received specification information packet and correspondence information packet, each receiving system selects desired content data from plural pieces of content to view the selected content data at the same time or in a switched manner.