To provide a wind velocity measuring system leading easily a frequency of a laser beam changed by a Doppler shift, and measuring easily and simply a wind velocity and a wind direction in a measuring portion.

This wind velocity measuring system is provided with: a laser beam generator 11 for emitting the laser beam L1; a half-mirror 24 for dispersing spectrally a return laser beam L2 of the emitted laser beam L1; the first light intensity measuring instrument 27 for measuring light intensity of the first dispersed return laser beam L21 transmitted through the half-mirror; an optical filter 26 for attenuating the second dispersed return laser beam L22 reflected by the half-mirror in response to the frequency; the second light intensity measuring instrument 28 for measuring light intensity of the second dispersed return laser beam L22 attenuated by the optical filter; and a control part for calculating the frequency of the return laser beam from an attenuation amount of the intensity by the optical filter, and for calculating the wind velocity and the wind direction in the measuring portion, by substitution with the frequency of the return laser beam together with the frequency of the emitted laser beam.