An apparatus for displaying sectional planes of a target object utilizing 3 dimensional (3D) ultrasound data. The apparatus is capable of scanning the target object in real time by improving a scan conversion speed and virtually scans the target object by storing previously acquired 3D data. The apparatus, which displays a target object by using 3D ultrasound data, includes 1) a scan conversion unit for performing scan conversion to convert Cartesian coordinates for display on a screen of a display device to conical coordinates of 3D data, and 2) a rendering unit for rendering multiple sectional plane images, based on the 3D scan conversion, parallel with a reference sectional plane.