An ophthalmological device comprising: a light source; a measurement optical system configured to emit light from the light source into an eye to be examined and to guide reflected light; a reference optical system configured to split light from the light source and generate reference light; a light receiving element configured to receive interfering light composed of the reflected light guided by the measurement optical system and the reference light generated by the reference optical system; and an arithmetic unit configured to calculate a dimension along an eye axis of a target portion of the eye from interfering light received by the light receiving element, the measurement optical system including: an incidence position changing member configured to change an incidence position of light emitted to the eye; and a driving unit configured to drive the incidence position changing member in a plane orthogonal to the optical axis so as to scan at the incidence position of emitted light in a predetermined region of the eye, wherein the predetermined region is a region where a straight line passes through when the straight line radially extended from a cornea apex of the eye is circumferentially moved over a predetermined angle range in the case of the eye is viewed from a front, and when the eye is viewed from a front, the predetermined angle range is an angle range of +20° to +85° and -20° to -85° where (+) is a clockwise direction and (-) is a counterclockwise direction with respect to a reference line that is a vertical line extended upward from the cornea apex of the eye, wherein the arithmetic unit is configured to specify a position of an anterior surface of the target portion and a position of a posterior surface of the target portion from interfering light received when light emitted to the eye is scanned in the predetermined region, and the arithmetic unit is configured to calculate a dimension along the eye axis of the target portion from the specified positions. a light source; a measurement optical system configured to emit light from the light source into an eye to be examined and to guide reflected light; a reference optical system configured to split light from the light source and generate reference light; a light receiving element configured to receive interfering light composed of the reflected light guided by the measurement optical system and the reference light generated by the reference optical system; and an arithmetic unit configured to calculate a dimension along an eye axis of a target portion of the eye from interfering light received by the light receiving element, the measurement optical system including: an incidence position changing member configured to change an incidence position of light emitted to the eye; and a driving unit configured to drive the incidence position changing member in a plane orthogonal to the optical axis so as to scan at the incidence position of emitted light in a predetermined region of the eye, wherein the predetermined region is a region where a straight line passes through when the straight line radially extended from a cornea apex of the eye is circumferentially moved over a predetermined angle range in the case of the eye is viewed from a front, and when the eye is viewed from a front, the predetermined angle range is an angle range of +20° to +85° and -20° to -85° where (+) is a clockwise direction and (-) is a counterclockwise direction with respect to a reference line that is a vertical line extended upward from the cornea apex of the eye, wherein the arithmetic unit is configured to specify a position of an anterior surface of the target portion and a position of a posterior surface of the target portion from interfering light received when light emitted to the eye is scanned in the predetermined region, and the arithmetic unit is configured to calculate a dimension along the eye axis of the target portion from the specified positions. an incidence position changing member configured to change an incidence position of light emitted to the eye; and a driving unit configured to drive the incidence position changing member in a plane orthogonal to the optical axis so as to scan at the incidence position of emitted light in a predetermined region of the eye, wherein the predetermined region is a region where a straight line passes through when the straight line radially extended from a cornea apex of the eye is circumferentially moved over a predetermined angle range in the case of the eye is viewed from a front, and when the eye is viewed from a front, the predetermined angle range is an angle range of +20° to +85° and -20° to -85° where (+) is a clockwise direction and (-) is a counterclockwise direction with respect to a reference line that is a vertical line extended upward from the cornea apex of the eye, wherein the arithmetic unit is configured to specify a position of an anterior surface of the target portion and a position of a posterior surface of the target portion from interfering light received when light emitted to the eye is scanned in the predetermined region, and the arithmetic unit is configured to calculate a dimension along the eye axis of the target portion from the specified positions.