Digital image transmission system transmitting digital image data

A digital image transmission system comprising a host device, a transmission and reception reinforcement device, and a display device, the host device transmitting digital image data to the display device by using the transmission and reception reinforcement device, wherein the transmission and reception reinforcement device comprises a transmitter, a receiver, and a power supply circuit, and the power supply circuit comprises a first power supply unit supplying power to the transmitter and a second power supply unit supplying power to the receiver, and power output terminals of the first and second power supply units are connected to each other, and external-power supply voltages respectively input to the first and second power supply units are output to the power output terminals, and when all of the external-power supply voltages input to the first and second power supply units are lower than a predetermined voltage, an internal-power supply voltage present in a communication line between the host device and the display device is output to the power output terminals.