A method of performing registration of medical images, comprising: mapping a virtual coordinate system used by a first medical apparatus and a virtual coordinate system used by a second medical apparatus to each other, wherein the virtual coordinate systems are associated with a real-time medical image captured by the first medical apparatus and a three-dimensional medical image previously captured by the second medical apparatus, respectively; detecting a position of a probe of the first medical apparatus in a virtual coordinate system used by the second medical apparatus, based on a result of the mapping; characterized in that, the method further comprises, selecting a reference cross-section from the three-dimensional medical image using the detected position of the probe; estimating a relative movement range of a scanning plane of the probe by using previously stored information about a range between a position in which an organ is moved by a patient's inhalation and a position in which the organ is moved by the patient's exhalation; selecting neighboring cross-sections that exist in the relative movement range estimated from the reference cross-section; reconstructing a volume image by accumulating the reference cross-section and neighboring cross sections; and extracting from the reconstructed volume image a cross-sectional image corresponding to the real-time medical image, wherein the cross-sectional image changes according to the patient's inhalation and exhalation, said extracting comprising: performing segmentation on an anatomical object appearing on the real-time medical image and the volume image, the anatomical object segmented from the volume image being a 3D object, and the anatomical object segmented from the real-time medical image corresponding to a 2D object; while rotating and moving the 2D object with respect to corresponding portions of the 3D object, extracting from the volume image a cross-section having a largest similarity between the anatomical object segmented in the real-time medical image and the volume image; reconstructing from the volume image a cross-sectional image corresponding to the extracted cross-section; and outputting the reconstructed cross-sectional image. mapping a virtual coordinate system used by a first medical apparatus and a virtual coordinate system used by a second medical apparatus to each other, wherein the virtual coordinate systems are associated with a real-time medical image captured by the first medical apparatus and a three-dimensional medical image previously captured by the second medical apparatus, respectively; detecting a position of a probe of the first medical apparatus in a virtual coordinate system used by the second medical apparatus, based on a result of the mapping; characterized in that, the method further comprises, selecting a reference cross-section from the three-dimensional medical image using the detected position of the probe; estimating a relative movement range of a scanning plane of the probe by using previously stored information about a range between a position in which an organ is moved by a patient's inhalation and a position in which the organ is moved by the patient's exhalation; selecting neighboring cross-sections that exist in the relative movement range estimated from the reference cross-section; reconstructing a volume image by accumulating the reference cross-section and neighboring cross sections; and extracting from the reconstructed volume image a cross-sectional image corresponding to the real-time medical image, wherein the cross-sectional image changes according to the patient's inhalation and exhalation, said extracting comprising: performing segmentation on an anatomical object appearing on the real-time medical image and the volume image, the anatomical object segmented from the volume image being a 3D object, and the anatomical object segmented from the real-time medical image corresponding to a 2D object; while rotating and moving the 2D object with respect to corresponding portions of the 3D object, extracting from the volume image a cross-section having a largest similarity between the anatomical object segmented in the real-time medical image and the volume image; performing segmentation on an anatomical object appearing on the real-time medical image and the volume image, the anatomical object segmented from the volume image being a 3D object, and the anatomical object segmented from the real-time medical image corresponding to a 2D object; while rotating and moving the 2D object with respect to corresponding portions of the 3D object, extracting from the volume image a cross-section having a largest similarity between the anatomical object segmented in the real-time medical image and the volume image; reconstructing from the volume image a cross-sectional image corresponding to the extracted cross-section; and outputting the reconstructed cross-sectional image.