A digital broadcasting system includes an authoring apparatus and a transmission apparatus. The authoring apparatus generates event information, which defines an event message that should be transmitted immediately after an operator's instruction to transmit the event message is received, and adds the event information to a content. The authoring apparatus then extracts the event information from the content by referring to tag information and transfers the extracted event information to the transmission apparatus. The transmission apparatus stores the event message defined by the event information transferred from the authoring apparatus. According to an operator's instruction to transmit the event message, the transmission apparatus issues the event message, and multiplexes and transmits the issued event message and the content.