In a contactless IC card system, a modulating circuit manufactured in an IC form is operable at a high power efficiency. The demodulating apparatus is configured to include: signal processing means for producing first and second input signals; first clamping circuit for clamping said first input signal; second clamping circuit for clamping said second input signal; first band limiting means for removing a component of said first input signal from an output signal of said first clamping circuit; second band limiting means for removing a component of said second input signal from an output signal of said second clamping circuit; and calculating means for adding, or averaging an output signal of said first band limiting means and an output signal of said second band limiting means.