An optical signal transmitting apparatus includes a light-emitting element, a light-receiving section, a conductive line and a controller. The light-emitting element converts an electric signal into an optical signal. The light-receiving section converts the optical signal, which is received from the light-emitting element through an optical transmission medium, into an electric signal. The conductive line is connected to an output terminal of the light-receiving section. The light-receiving section outputs an analog signal through the output terminal. The controller controls an extinction ratio of the light-emitting element in accordance with a characteristic impedance of the conductive line.