An apparatus has an optical system detecting spectral information and having an optical scanner (23) and a driving unit (50) changing the optical path length by moving an optical member (31), a monitor (75), a control unit (70) obtaining a tomographic image by performing Fourier analysis on the information and displaying the obtained image, and a unit previously setting an image on the monitor, in which the member is moved from an initial position and presence or absence of the tomographic image is determined, when the presence is detected, whether the tomographic image is normal or inverted is determined, and when the tomographic image is not the set image, the member is moved to obtain the set image, and when the tomographic image is the set image, the member is moved so that a position of the tomographic image in the depth direction coincides with a predetermined adjustment position and the driving unit is stopped.
