A three-dimensional intra-oral scanner comprising: a case having a front surface including a light outlet and a light inlet; a light output unit disposed in the case and configured to output light into an oral cavity through the light outlet; an image sensing unit disposed in the case and configured to acquire 2D scan image of a tooth in the oral cavity from reflected light incident through the light inlet; a reflector member configured to be detachably installed on the case includes a reflector configured to reflect light output through the light outlet into the oral cavity and to reflect reflected light reflected from the oral cavity to the light inlet when installed in the case; a 3D scan data generator configured to generate 3D scan data using the 2D scan image acquired by the image sensing unit, wherein, the 2D scan image acquired from the reflected light, reflected by the reflector, by the image sensing unit when the reflector member is installed on the case is referred to as 2D scan image of a narrow area and the 2D scan image acquired from the entire reflected light incident through the light inlet by the image sensing unit when the reflector member is not installed on the case is referred to as 2D scan image of a wide area, the 3D scan data generator generates 3D scan data using the 2D scan image of the wide area when the reflector member is not installed on the case, and generates the 3D scan data using the 2D scan image of the narrow area when the reflector member is installed on the case, characterized in that, the 3D intra-oral scanner includes a 3D model data generator configured to generate 3D model data bv registering the 3D scan data of a wide area and to register the 3D scan data of a narrow area to the 3D model data, wherein the 3D scan data of the wide area correspond to the 3D scan data generated bv the 3D scan data generator using the 2D scan image of the wide area, and wherein the 3D scan data of a narrow area correspond to the 3D scan data generated bv the 3D scan data Generator usinq the 2D scan imaqe of the narrow area. a case having a front surface including a light outlet and a light inlet; a light output unit disposed in the case and configured to output light into an oral cavity through the light outlet; an image sensing unit disposed in the case and configured to acquire 2D scan image of a tooth in the oral cavity from reflected light incident through the light inlet; a reflector member configured to be detachably installed on the case includes a reflector configured to reflect light output through the light outlet into the oral cavity and to reflect reflected light reflected from the oral cavity to the light inlet when installed in the case; a 3D scan data generator configured to generate 3D scan data using the 2D scan image acquired by the image sensing unit, wherein, the 2D scan image acquired from the reflected light, reflected by the reflector, by the image sensing unit when the reflector member is installed on the case is referred to as 2D scan image of a narrow area and the 2D scan image acquired from the entire reflected light incident through the light inlet by the image sensing unit when the reflector member is not installed on the case is referred to as 2D scan image of a wide area, the 3D scan data generator generates 3D scan data using the 2D scan image of the wide area when the reflector member is not installed on the case, and generates the 3D scan data using the 2D scan image of the narrow area when the reflector member is installed on the case, characterized in that, the 3D intra-oral scanner includes a 3D model data generator configured to generate 3D model data bv registering the 3D scan data of a wide area and to register the 3D scan data of a narrow area to the 3D model data, wherein the 3D scan data of the wide area correspond to the 3D scan data generated bv the 3D scan data generator using the 2D scan image of the wide area, and wherein the 3D scan data of a narrow area correspond to the 3D scan data generated bv the 3D scan data Generator usinq the 2D scan imaqe of the narrow area.