1. An optical coherence tomography observation apparatus, comprising: an interference optical system that has a splitting device that is configured to split incident light into reference light and illumination light, and an optical combining device that is configured to make the reference light and a measurement light interfere with each other, the measurement light being obtained from an observation object which is illuminated with the illumination light, the interference optical system having function as an illumination optical system and as an observation optical system, the illumination optical system being configured to illuminate the observation object with the illumination light, the observation optical system being configured to observe the measurement light; a light detection unit that is configured to detect interference light obtained from the interference by the optical combining device; a light control unit that is configured to change a plurality of numerical apertures, at least one optical system of the illumination optical system and the observation optical system having the light control unit; an image generator that is configured to generate a first tomographic image which is within a first observation range of the observation object based on first interference light and to generate second tomographic images which are within a second observation range of the observation object based on second interference light, the first interference light being detected by the light detection unit in a state where the light control unit is set to a first numerical aperture, the second interference light being detected by the light detection unit in a state where the light control unit is set to a second numerical aperture which is larger than the first numerical aperture, the second observation range being smaller than the first observation range, a position of the second tomographic image in the observation object is moved in a depth direction of the observation object; and a detector that is configured to detect a relative position for each of the second tomographic image generated by the image generator with respect to the first tomographic image generated by the image generator, at which a correlation of the second tomographic image with the first tomographic image becomes highest.