1. An ultrasound diagnosis apparatus, comprising: an ultrasound probe; and a processor configured to generate volume data including a structure in an object based on an output of the ultrasound probe, set a viewing point and a viewing direction to the volume data, generate virtual endoscopy image data of the structure from the volume data based on the viewing point and the viewing direction set to the volume data, set a marker on the virtual endoscopy image data by input from an operator, set a reference line passing the viewing point to the volume data based on a position of the marker on the virtual endoscopy image data, determine a reference point in the volume data where the reference line and a surface of the structure cross, set at least one multi-planar-reconstruction (MPR) cross-sectional plane to the volume data based on the reference point, generate at least one MPR image data from the volume data, the MPR image data corresponding to the MPR cross-sectional plane, and cause a display to display both the virtual endoscopy image data and the MPR image data.