A semiconductor integrated circuit includes an input circuit for taking in signals and an output circuit for outputting signals. The input circuit is so set that the input impedance during input signal transition is lower than the input impedance on other occasions than input signal transition. The output circuit is so set that the driving force during the second half of signal transition is lower than the driving force during the first half of transition. Such setting that the input impedance during input signal transition is lower than the input impedance on other occasions than input signal transition reduces reflected waves during input signal transition. Such setting that the driving force during the second half of signal transition is lower than the driving force during the first half of transition suppresses production of reflected waves during the second half of signal transition. Thus, the necessity for external components, such as damping resistors and terminator resistors, for impedance matching is obviated.