PURPOSE: To reduce insertion loss of the elastic surface wave, by giving a characteristic, where a linear chirp waveform is generated, to each block of plural transducer electrodes and by giving phase difference 90° to read screen type electrodes of each block.

CONSTITUTION: In respect to transducer electrode 11, the distance between reed screen type electrodes (a) and (b) is set to (n+1/4)λ for the purpose of obtaining a chirp signal for every block of blocks B1∼B4, and the interval of electrode fingers is changed successively for every block of blocks B1∼B4 to obtain a unidirectional dispersive delay line. Phase shifter 12 gives phase difference 90° between electrodes (a) and (b) to satisfy the unidirectional condition for every block. The similar constitution is adopted for output-side transducer 13.