A surface acoustic wave device includes a piezoelectric substrate, first and second input transducers formed on the substrate and adapted for respectively generating surface acoustic waves corresponding to input signals, the first and second input transducers each having a shape to focus the surface acoustic waves generated thereby, an output transducer formed between the first and second input transducers on the substrate and adapted for obtaining a convolution -signal of the surface acoustic waves generated by the first and second input transducers, and conductive films, one formed between the first input transducer and the output transducer and another between the second input transducer and the output transducer on the substrate. A communication system includes a transmitter for transmitting a signal modulated according to information, a circuit for receiving the modulated signal transmitted from the transmitter, a circuit for generating a reference signal, a surface acoustic wave device, as described above, for outputting a convolution signal of the modulated signal and the reference signal, and a demodulating circuit for restoring the information, using the convolution signal output from the surface acoustic wave device.