An ophthalmologic apparatus comprising: an optical system that acquires data of an anterior segment of a subject's eye or a fundus (Ef) of the subject's eye; an imaging unit that images the anterior segment or the fundus (Ef), wherein the imaging unit acquires a first image and a second image at different timings from each other; a movement mechanism that moves the subject's eye and the optical system relative to each other; and a controller that controls the movement mechanism so as to maintain a positional relationship between the subject's eye and the optical system based on an anterior segment image acquired by the imaging unit in an anterior segment mode for acquiring data of the anterior segment by the optical system, and controls the movement mechanism so as to maintain the positional relationship based on a fundus image acquired by the imaging unit in a fundus mode for acquiring data of the fundus (Ef) by the optical system, a first rotational movement amount calculator that calculates a first rotational movement amount between a partial image in the second image and a corresponding partial image in the first image, the corresponding partial image corresponding to the partial image; and a first registration unit that performs registration between the corresponding partial image and the partial image in a rotation direction based on the first rotational movement amount; characterized in that the ophthalmologic apparatus further comprises: an analyzer that specifies a characteristic region in the anterior segment image, wherein the controller controls the movement mechanism based on a displacement of the characteristic region with respect to a reference position in the anterior segment image in the anterior segment mode; a first parallel movement amount calculator that performs a phase only correlation processing on the corresponding partial image and the partial image registered by the first registration unit to calculate a first parallel movement amount between the corresponding partial image and the partial image, and in the anterior segment mode, the controller determines whether or not to be capable of maintaining the positional relationship based on the displacement, and controls the movement mechanism based on the first parallel movement amount when it is determined that maintaining the positional relationship is impossible. an optical system that acquires data of an anterior segment of a subject's eye or a fundus (Ef) of the subject's eye; an imaging unit that images the anterior segment or the fundus (Ef), wherein the imaging unit acquires a first image and a second image at different timings from each other; a movement mechanism that moves the subject's eye and the optical system relative to each other; and a controller that controls the movement mechanism so as to maintain a positional relationship between the subject's eye and the optical system based on an anterior segment image acquired by the imaging unit in an anterior segment mode for acquiring data of the anterior segment by the optical system, and controls the movement mechanism so as to maintain the positional relationship based on a fundus image acquired by the imaging unit in a fundus mode for acquiring data of the fundus (Ef) by the optical system, a first rotational movement amount calculator that calculates a first rotational movement amount between a partial image in the second image and a corresponding partial image in the first image, the corresponding partial image corresponding to the partial image; and a first registration unit that performs registration between the corresponding partial image and the partial image in a rotation direction based on the first rotational movement amount; characterized in that the ophthalmologic apparatus further comprises: an analyzer that specifies a characteristic region in the anterior segment image, wherein the controller controls the movement mechanism based on a displacement of the characteristic region with respect to a reference position in the anterior segment image in the anterior segment mode; a first parallel movement amount calculator that performs a phase only correlation processing on the corresponding partial image and the partial image registered by the first registration unit to calculate a first parallel movement amount between the corresponding partial image and the partial image, and in the anterior segment mode, the controller determines whether or not to be capable of maintaining the positional relationship based on the displacement, and controls the movement mechanism based on the first parallel movement amount when it is determined that maintaining the positional relationship is impossible. an analyzer that specifies a characteristic region in the anterior segment image, wherein the controller controls the movement mechanism based on a displacement of the characteristic region with respect to a reference position in the anterior segment image in the anterior segment mode; a first parallel movement amount calculator that performs a phase only correlation processing on the corresponding partial image and the partial image registered by the first registration unit to calculate a first parallel movement amount between the corresponding partial image and the partial image, and in the anterior segment mode, the controller determines whether or not to be capable of maintaining the positional relationship based on the displacement, and controls the movement mechanism based on the first parallel movement amount when it is determined that maintaining the positional relationship is impossible.