An interface circuit includes: a plurality of signal transmitter circuits each receiving an input signal and outputting an output signal responsive to a first power supply voltage based on the input signal; an operation control circuit controlling operation/suspension of the signal transmitter circuits; and an amplitude control circuit exerting control so that the first power supply voltage be greater with increase in the number of operating circuits among the signal transmitter circuits and thereby the amplitude of the output signals of the signal transmitter circuits become greater.