Overlay measurement device and method

The overlay measurement device according to the present invention is used for measuring an interlayer overlay error of a sample on which overlay marks are formed, and is characterized by comprising: a height difference detection optical system for detecting a height difference ([delta] h) between a first overlay mark and a second overlay mark; an illumination optical system that illuminates an overlay mark on the sample; a main beam splitter that splits reflected light from the overlay mark into a first light beam and a second light beam; the first detector receives the first light beam and generates a first overlay mark image focused on the first overlay mark; the second detector receives the second light beam and generates a second overlay mark image focused on the second overlay mark; an imaging optical system that images the first light beam on the first detector; and a telecentric imaging optical system that includes an optical path adjustment unit that adjusts the length of the optical path of the secon