Disclosed is a data delivery control system capable of allowing for data delivery to a large number of client terminal devices without imposing a heavy load on the network by flexibly dealing with the network configuration.The data delivery control system includes at least one second client terminal device among a plurality of client terminal devices and a data delivery control device. The second client terminal device includes a terminal detection unit that detects at least one logically proximate first client terminal device to which delivery data received from a server device can be transferred, and a terminal-to-terminal data transfer unit that transfers the delivery data to the at least one first client terminal device. The data delivery control device includes a data delivery unit that delivers the delivery data to the at least one second client terminal device.