PURPOSE: To realize a frequency analyzer which has a wide band and high resolution while eliminating a failure in frequency detection, by constituting two optical circuits in pointal symmetry on the same substrate, and then using a lens system and a elastic surface wave energizing electrode in common.

CONSTITUTION: The output light of a semiconductor laser 15 is passed through a lens 16 to obtain parallel light, which is deflected by a Bragg diffraction grating, formed by a elastic surface wave energized by applying a signal to be measured to a elastic surface wave electrode 20, and then focused through a lens 18 and detected by a phtodetecting element group 19. Similarly, the output light of a semiconductor laser 15' is collimated by the lens 18 and deflected, and the deflected light is focused by a lens 15 by the lens 16 and detected by a photodetecting element group 19'. Consequently, the propagation direction of the elastic surface wave is changed automatically to respective optical circuits under the best condition at the same time according to variation in frequency, and the evil influence of unnecessary scattered light is reduced.