PURPOSE: To decrease the electric resistance and to reduce the loss, by providing a unit unidirectional electrode having greater electrode finger width toward the elastic surface wave propagating direction of a common electrode.

CONSTITUTION: A width L' of a meander line electrode 8 of a unit unidirectional converter is taken as 3/2 wavelength. Further, the elastic surface wave energizied at electrodes 6, 8 and that energized at electrode 7, 8 are in the same phase relation as conventional devices for the center response frequency, they energize the elastic surface waves in the arrow direction and cancel the opposite direction. Thus, spurious response can be suppressed by locating conventional unidirectional converters at the input side and said unidirectional converter at the output side.