In optical tomography measurement using light, the wavelength of which is periodically swept, interference light between reflection light and reference light is split into first interference light and second interference light by a light splitting means. The optical path length of the first interference light and that of the second interference light are adjusted by an interference-light optical path length adjustment means so that they become the same. Further, balanced detection is performed on the first interference light and the second interference light by an interference light detection means.
