A data transmission device, method, and program therefor that effectively increase throughput even when a delay increase occurs due to a cause other than congestion in the network. The data transmission device (11) is provided with a transmission unit (60) which transmits to a user terminal (30) data requested over a network (20). The data transmission device includes a transmission rate control element (51C) which controls the transmission rate on the basis of the degree of congestion detected by a congestion detection element (51B) during delay measurement by a delay measurement processing unit (40), and a reference value correction processing element (51D) which temporarily corrects the detection criteria used by the congestion detection element; when it has been determined that the delay has increased due to a cause other than congestion. This reference value correction element increases the accuracy of detection processing by the congestion detection element, thereby improving throughput.