A spectral measurement method of the present invention includes: a measuring step of measuring optical spectra of some sections specified among a plurality of sections on a specimen; a scalar-value calculating step of calculating, for individual measured sections, scalar values that represent information contained in the obtained optical spectra; an interpolating step of interpolating scalar values of unmeasured sections by using the calculated scalar values and by using two types of interpolation methods; an identifying step of identifying sections in which absolute values of differences between the two scalar values interpolated by using the two types of interpolation methods are equal to or greater than a predetermined threshold; and a repeating step of re-executing steps from the measuring step to the identifying step after specifying the identified sections.