1. An ultrasonic imaging apparatus comprising: a 3D tomographic image data capturing device configured to capture 3D tomographic image data from a 3D region inside a subject; a region-of-interest setting device configured to set a 3D region of interest corresponding to the 3D region in an image memory that stores the 3D tomographic image data; a surface image extracting device configured to extract data on a surface image of a tissue included in the 3D region using the 3D tomographic image data, wherein the surface image is within the 3D region of interest; a stereoscopic display generating device configured to generate stereoscopic display data to display the surface image data stereoscopically; a plane formation device configured to form 2D image data according to the 3D tomographic image data; and a display device configured to display the stereoscopic display data, wherein said region-of-interest setting device is further configured to: display a 2D tomographic image of a 2D region including the tissue on said display device using the 2D image data; receive a manual setting of two markers indicating a periphery of the tissue in the 2D tomographic image; define a tissue boundary as a line connecting the two markers in the 2D tomographic image; define a first line segment on a first side of the tissue boundary line and a second line segment on a second side of the tissue boundary line such that the tissue boundary line is substantially equidistance between the first line segment and the second line segment to at least partially define a 2D region of interest; and generate the 3D region of interest by expanding the 2D region of interest in the 2D tomographic image in a mechanical scan direction and including the tissue boundary in the vicinity of the center.