1. An OCT apparatus for obtaining a tomogram using optical interference between signal light and reference light, comprising: an obtaining unit configured to obtain a position of a specific image with respect to a coherence gate from a first tomogram obtained by imaging; a moving unit configured to move the coherence gate by a set moving distance along a predetermined moving direction; and a determination unit configured to determine a positional relationship between the specific image and the coherence gate based on the position of the specific image with respect to the coherence gate obtained from a second tomogram obtained by imaging after movement of the coherence gate and the position obtained by said obtaining unit.