A surface acoustic wave signal processing apparatus for processing first and second high-frequency signals having frequencies f.sub.1 and f.sub.2 respectively, which comprises: first and second surface acoustic wave delay elements for receiving the first and second high-frequency signals respectively and independently of each other, the delay elements being formed as surface acoustic wave excitation and reception transducers on a piezoelectric substrate so that a phase delay .phi..sub.1 with respect to the frequency f.sub.1 is substantially equal to a phase delay .phi..sub.2 with respect to the frequency f.sub.2 (that is, .phi..sub.1 .apprxeq..phi..sub.2); and a mixer for mixing first and second high-frequency output signals of the first and second surface acoustic wave delay elements so that a signal having a frequency .vertline.f.sub.1 -f.sub.2 .vertline. which is a difference between the two frequencies f.sub.1 and f.sub.2 is taken out as an output signal of the mixer.