A displacement measurement method comprising the steps of: emitting light having a dispersed spectrum from a point light source; subjecting the light to axial chromatic aberration and collecting the light subjected to axial chromatic aberration on a measurement object by an optical element (1, 2); passing that portion of the light collected by the optical element (1, 2) that is focused on the measurement object through an aperture; obtaining a spectrum of the light that has passed through the aperture; obtaining spectral reflectance characteristics of the measurement object; and measuring a distance between the optical element (1, 2) and the measurement object based on a peak wavelength of the spectrum; wherein the distance is measured using the obtained spectral reflectance characteristics while mitigating an error caused by the spectral reflectance characteristics affecting the measurement of the distance, and wherein the step of obtaining spectral reflectance characteristics of the measurement object includes the step of: changing the distance between the optical element (1, 2) and the measurement object, and acquiring for each distance a local maximum point of the spectrum of the light that has passed through the aperture; the method further comprising the steps of: detecting a distance between the optical element (1, 2) and the measurement object at which the local maximum point of the spectrum of the light that has passed through the aperture is a local maximum point or a local minimum point in the spectral reflectance characteristics; and setting the detected distance as a reference distance between the optical element (1, 2) and the measurement object when the displacement is measured. emitting light having a dispersed spectrum from a point light source; subjecting the light to axial chromatic aberration and collecting the light subjected to axial chromatic aberration on a measurement object by an optical element (1, 2); passing that portion of the light collected by the optical element (1, 2) that is focused on the measurement object through an aperture; obtaining a spectrum of the light that has passed through the aperture; obtaining spectral reflectance characteristics of the measurement object; and measuring a distance between the optical element (1, 2) and the measurement object based on a peak wavelength of the spectrum; wherein the distance is measured using the obtained spectral reflectance characteristics while mitigating an error caused by the spectral reflectance characteristics affecting the measurement of the distance, and wherein the step of obtaining spectral reflectance characteristics of the measurement object includes the step of: changing the distance between the optical element (1, 2) and the measurement object, and acquiring for each distance a local maximum point of the spectrum of the light that has passed through the aperture; the method further comprising the steps of: detecting a distance between the optical element (1, 2) and the measurement object at which the local maximum point of the spectrum of the light that has passed through the aperture is a local maximum point or a local minimum point in the spectral reflectance characteristics; and setting the detected distance as a reference distance between the optical element (1, 2) and the measurement object when the displacement is measured. changing the distance between the optical element (1, 2) and the measurement object, and acquiring for each distance a local maximum point of the spectrum of the light that has passed through the aperture; the method further comprising the steps of: detecting a distance between the optical element (1, 2) and the measurement object at which the local maximum point of the spectrum of the light that has passed through the aperture is a local maximum point or a local minimum point in the spectral reflectance characteristics; and setting the detected distance as a reference distance between the optical element (1, 2) and the measurement object when the displacement is measured. detecting a distance between the optical element (1, 2) and the measurement object at which the local maximum point of the spectrum of the light that has passed through the aperture is a local maximum point or a local minimum point in the spectral reflectance characteristics; and setting the detected distance as a reference distance between the optical element (1, 2) and the measurement object when the displacement is measured.