An apparatus, comprising: a coherent light source configured to emit coherent light in a first wavelength range; another coherent light source configured to emit coherent light in a second wavelength range different from the first wavelength range, wherein the coherent light source and the other coherent light source are configured to alternately emit their coherent light; an irradiation light control unit configured to collimate the coherent light, adapt an irradiation diameter of the coherent light and emit the coherent light to a measurement target containing scatterers; a light receiving element; an incident angle limiting unit configured to limit an incident angle of scattered light that is incident on any single point of the light receiving element to a value of 10 ° or less, wherein the scattered light is light scattered by the scatterers; and a processing means configured to: separate a beat signal output by the light receiving element into a first beat signal generated by a first part of the scattered light and a second beat signal generated by a second part of the scattered light, the first part of the scattered light being generated by the scatterers by scattering the coherent light in the first wavelength range, and the second part of the scattered light being generated by the scatterers by scattering the coherent light in the second wavelength range; calculate a first power spectrum for the first beat signal; calculate a second power spectrum for the second beat signal; normalize the first power spectrum and the second power spectrum; input the normalized first power spectrum and normalized second power spectrum to an adaptive filter; and determine velocity information for the scatterers based on a power spectrum of a beat signal output from the adaptive filter. a coherent light source configured to emit coherent light in a first wavelength range; another coherent light source configured to emit coherent light in a second wavelength range different from the first wavelength range, wherein the coherent light source and the other coherent light source are configured to alternately emit their coherent light; an irradiation light control unit configured to collimate the coherent light, adapt an irradiation diameter of the coherent light and emit the coherent light to a measurement target containing scatterers; a light receiving element; an incident angle limiting unit configured to limit an incident angle of scattered light that is incident on any single point of the light receiving element to a value of 10 ° or less, wherein the scattered light is light scattered by the scatterers; and a processing means configured to: separate a beat signal output by the light receiving element into a first beat signal generated by a first part of the scattered light and a second beat signal generated by a second part of the scattered light, the first part of the scattered light being generated by the scatterers by scattering the coherent light in the first wavelength range, and the second part of the scattered light being generated by the scatterers by scattering the coherent light in the second wavelength range; calculate a first power spectrum for the first beat signal; calculate a second power spectrum for the second beat signal; normalize the first power spectrum and the second power spectrum; input the normalized first power spectrum and normalized second power spectrum to an adaptive filter; and determine velocity information for the scatterers based on a power spectrum of a beat signal output from the adaptive filter. separate a beat signal output by the light receiving element into a first beat signal generated by a first part of the scattered light and a second beat signal generated by a second part of the scattered light, the first part of the scattered light being generated by the scatterers by scattering the coherent light in the first wavelength range, and the second part of the scattered light being generated by the scatterers by scattering the coherent light in the second wavelength range; calculate a first power spectrum for the first beat signal; calculate a second power spectrum for the second beat signal; normalize the first power spectrum and the second power spectrum; input the normalized first power spectrum and normalized second power spectrum to an adaptive filter; and determine velocity information for the scatterers based on a power spectrum of a beat signal output from the adaptive filter.