An optical interferometric measurement apparatus including a wavelength-swept light source and including an interference optical system having a first interference optical system and a second interference optical system , the interference optical system adapted to output a monitoring interference signal S(t) from the first interference optical system and a measurement interference signal S(t) from the second interference optical system in accordance with light emitted from the wavelength-swept light source , and including a controller receiving both signals and adapted to measure a movement of an object to be measured , characterized in that the controller comprises: a storage being adapted to store monitoring data acquired by sampling the monitoring interference signal S(t) in each period T of the light source and measurement data acquired by sampling the measurement interference signal S(t) in each period T of the light source ; a calculator being adapted to calculate a departure (sh) of a sweep start frequency fs from an average value of the sweep start frequencies fs in each period T based on the monitoring data and to convert the calculated departures into differences in the number of sampling points; and a Fourier transformation unit being adapted to apply Fourier transform to the measurement data in each period T, wherein the calculator is further adapted to define a maximum difference in the number of sampling points and to align a sampling width H of the measurement data in each period T by removing data as many as the defined maximum difference in the number of sampling points from a sampling start point and retroactively from a sampling end point, said Fourier transformation unit is further adapted to apply said Fourier transform to the measurement data the width H of which has been aligned by the calculator , and the controller is further adapted to determine a phase φ of the measurement interference signal S(t) based on the Fourier-transformed measurement data and to measure the movement of the object based on the determined phase . a storage being adapted to store monitoring data acquired by sampling the monitoring interference signal S(t) in each period T of the light source and measurement data acquired by sampling the measurement interference signal S(t) in each period T of the light source ; a calculator being adapted to calculate a departure (sh) of a sweep start frequency fs from an average value of the sweep start frequencies fs in each period T based on the monitoring data and to convert the calculated departures into differences in the number of sampling points; and a Fourier transformation unit being adapted to apply Fourier transform to the measurement data in each period T, wherein the calculator is further adapted to define a maximum difference in the number of sampling points and to align a sampling width H of the measurement data in each period T by removing data as many as the defined maximum difference in the number of sampling points from a sampling start point and retroactively from a sampling end point, said Fourier transformation unit is further adapted to apply said Fourier transform to the measurement data the width H of which has been aligned by the calculator , and the controller is further adapted to determine a phase φ of the measurement interference signal S(t) based on the Fourier-transformed measurement data and to measure the movement of the object based on the determined phase . <EOS>