To provide a content-transmitting device, a reproducing device, etc., that realize synchronization, even when the same content are reproduced by a plurality of devices at remote places or via a transmission line with heavy communication traffic and perform stable synchronization, even when a communication line is loaded and the transmission time is made different from each another.

Reception sides 20 and 30 send echoes back as signals, indicating that a timer frame sent from a transmission side 10 has been received and a difference time calculating means 15 of the transmission side calculates the transmission delay time and adds correction information, when a timer frame is sent to the reproduction sides next to increase precision of a system clock among devices, while taking into consideration the delay time due to the lengths of different transmission lines, communication traffic, etc.