The present invention relates to a system for forming 3-dimensional images, including: an image data forming unit for forming 3-dimensional volume data based on image signals an image forming unit for forming multiple sectional plane images sliced along a predetermined direction in a 3-dimensional image, the image forming unit being configured to form at least one 3-dimensional image with partial 3-dimensional volume data selected by using the multiple sectional plane images from the 3-dimensional volume data, and a displaying unit for displaying the multiple sectional plane images and the 3-dimensional image.