A serial communication apparatus includes a slew rate control circuit, an output circuit, a detection circuit, and a switching circuit. The slew rate control circuit has a predetermined impedance, and supplies a constant current from an output according to an input signal. In the output circuit, first capacitance is charged and discharged by the constant current from the slew rate control circuit. The output circuit outputs a digital signal from an output terminal according to a drive voltage. The noise detection circuit detects noise propagated from the output terminal, and outputs a switching signal according to a detection result. The switching circuit switches an impedance of the slew rate control circuit to a value smaller than the predetermined impedance according to the switching signal.