A SAW sensor includes a substrate, first and second IDT on the substrate and a detector portion between the first and second IDT. The first IDT generates a surface acoustic wave in response to a high-frequency signal input. The second IDT receives the SAW from the first IDT, and converts the SAW to an electric signal and outputs the electric signal. A one pulse signal, which is input to the first IDT electrode, has an applying time that is at least as long as a delay time of a surface acoustic wave at the detector less an arrival time of a direct wave attributable to electromagnetic coupling between the first IDT and the second IDT electrode, and that is less than an arrival time at the second IDT of a third response wave of the surface acoustic wave from the first IDT.