An ultrasonic diagnostic apparatus has an ultrasonic endoscope, an ultrasonic observing portion, a position detecting unit, a monitor, a keyboard, and a mouse. Cross-sectional planes in parallel therewith are set to radial tomographic images, an intersecting line segment is obtained between a radial tomographic image and the cross-sectional plane, the intersecting line segments are combined, and a route tomographic image is generated. It is easily recognized how the lesion is spreading along the luminal portion during the examination by advancing and returning a radial scanning ultrasonic probe. Further, which part in the luminal portion is scanning during the examination can easily be recognized during the examination.