1. An ophthalmologic apparatus, comprising: a tomographic image acquiring unit configured to acquire a tomographic image of a fundus of an eye to be inspected, the tomographic image being a two-dimensional image including a depth direction of the fundus of the eye to be inspected; an evaluation index calculation unit configured to calculate an image evaluation index of the tomographic image; a tilt calculation unit configured to calculate a tilt of a first tomographic image acquired by the tomographic image acquiring unit; a relative position changing unit configured to change a relative position between the tomographic image acquiring unit and the eye, by relatively moving the tomographic image acquiring unit in a plane perpendicular to an optical axis of the tomographic image acquiring unit, based on the tilt of the first tomographic image, so as to reduce the tilt of a second tomographic image acquired by the tomographic image acquiring unit, wherein the second tomographic image is acquired after the first tomographic image is acquired; and a display control unit configured to cause a display unit to display information that the relative position is changed by the relative position changing unit, wherein the tilt of the second tomographic image is reduced such that the image evaluation index of the second tomographic image is greater than the image evaluation index of the first tomographic image.