Disclosed is a technique for effectively transmitting a plurality of contents under the situation securing minimum QoS. According to the technique, among a plurality of contents to be transmitted to a data reception device, two or more contents are set as main contents, and the remaining contents are set as stand-by contents. One of the two or more main contents is set as a broadcasting content to be broadcasted actually, and the remaining main content is set as a switching content. The data transmission device transmits the two main contents to the data reception device via a high-quality line (main content line) and transmits the remaining stand-by contents via a line of a quality lower than the main content line (proxy data transmission line). Contents are switched by interchanging between a broadcasting content and a switching content and interchanging between a switching content and a stand-by content.