Provided are a transmitting device connected to a receiving device via a channel and the receiving device connected to the transmitting device via a channel. The transmitting device connected to a receiving device includes: a transmitter connected to the channel via an output node and configured to transmit, via the channel, a transmission signal to the receiving device, the transmitter having a transmission impedance associated therewith that is variable; and a monitoring device configured to detect a channel impedance of the channel and a receiving impedance of the receiving device by monitoring a voltage level of the output node, the monitoring device configured to set the transmission impedance based on the channel impedance and the receiving impedance.