The present invention discloses an electric signal outputting apparatus in a serial electric transmission system. The electric signal outputting apparatus includes a switching part for switchably generating high and low output signals in accordance with signal data and transmitting the output signals to a transmission path, an impedance matching part for matching an output impedance to the impedance of the transmission path, and an auxiliary switching part for subsidiarily supplying current to an output node in the transmission path and subsidiarily absorbing current from the output node in the transmission path when the switching part switches the generation between high and low output signals, wherein the auxiliary switching part conducts the supplying and the absorbing for a period shorter than a pulse width of a reference clock of the serial electric transmission system.