When frequencies used in the two-frequency measurement of a SAW sensor are represented by f1 and f2 (f2>f1), an electrical signal processing device is provided without use of oversampling at a frequency higher than twice the frequency f2 or a two-system low-frequency conversion circuit, in which temperature compensation with the same accuracy as the case where these are used can be realized. Narrow band frequency filtering is applied to a waveform after roundtrips in a delay line type SAW sensor capable of transmitting and receiving multiple frequencies, the two frequencies f1 and f2 (f2>f1) are extracted, and a delay time is determined utilizing an aliasing obtained by applying undersampling at a frequency lower than twice the frequency f1.