In a transmission device connected by AC coupling, time taken before the start of transmission of valid data is shortened. The transmission device includes an internal resistor, an internal circuit, and a transmission-side control unit. One end of the internal resistor is connected to an output terminal connected to a capacitor. The internal circuit supplies one of a plurality of potentials different from each other to another end of the internal resistor. The transmission-side control unit performs control to supply one of the plurality of potentials to the internal circuit over a period from time when a potential of the output terminal is initialized to a predetermined initial value to timing when the potential of the output terminal reaches a predetermined specified value.