In a communication system comprising a communication device and a reproduction device capable of carrying out data communication with the communication device, the reproduction device includes a first storage unit in which content data are stored and a first communication unit engaged in data communication with the communication device, whereas the communication device in the communication system includes a second storage unit in which content data are stored, a second communication unit engaged in data communication with the first communication unit and a priority ranking determining unit that, based upon information obtained through the data communication and a priority ranking criterion, determines priority rankings for individual sets of content data in a content data group that includes both the content data stored in the first storage unit and the content data stored in the second storage unit.