PROBLEM TO BE SOLVED: To provide a signal processing apparatus for a surface acoustic wave (SAW) sensor capable of detecting influences of DC offset without using a circuit elements which may become a noise source or a signal attenuation source, as further as possible, and a signal processing method.SOLUTION: A receiver 3 receives a leakage differential signal from a transmitter 2 via a transmission/reception changeover switch 4. When a reference signal is leaked to the side of a SAW device 6, the receiver 3 receives a reflection signal of the leak from a low-noise amplifier 107. A differential signal transmitted by the transmitter 2 is transmitted by bringing a phase inversion switch 102 into a forward/backward state, and the receiver 3 receives signals while bringing the phase inversion switches 102 into the same state as each other. At the side of the receiver 3, the leakage differential signal from the transmission/reception changeover switch 104 and the leak signal of the reference signal become the same
