To prevent occurrence of a transmission error by suppressing the effect of noise on a transmission cable in the case that a personal computer downloads data to an image display device via the transmission cable.

A transmission repeater 7 is interposed between a 1st connector 51 of a transmission cable 30 to be connected to a personal computer 1 and a 2nd connector 5 of the transmission cable 30 to be connected to an image display device 2 closer to the 2nd connector 5 to the utmost. The transmission repeater 7 is provided with a driver 73 that applies voltage conversion to a received pulse wave signal and with filter circuits 8 through which the pulse wave signal outputted from the drier 73 pass. Each filter circuit 8 consists of a series connection of a pre-stage filter and a post-stage filter, and each of the pre-stage and post-stage filters is provided with an integration circuit and an inverter circuit.