The invention is to provide a wavelength dispersion measuring method for an optical fiber capable of measuring a wavelength dispersion in a section extending from an incident end of the optical fiber to an arbitrary point along the way by using a scattering phenomenon in which a scattering coefficient at a local point on the optical fiber is independent of time. Incident light having a known spectral density function S(.omega.) is caused to be incident on the optical waveguide, and a wavelength dispersion of the section extending from the incident end of the optical waveguide to the arbitrary point along the way by a correlational function between a signal being proportional to a scattered light amplitude generated at a first halfway point and a signal being proportional to a scattered light amplitude generated at a second halfway point.