1. An ultrasonic diagnosis apparatus comprising ultrasonic image generating means for reconstructing an ultrasonic image from reflection echo signals output from an ultrasonic probe, storing means for storing volume image data pre-obtained by a diagnostic imaging apparatus; reference-image generating means for extracting tomographic image data corresponding to a scan plane of the ultrasonic wave from the volume image data stored in the storing means and reconstructing a reference image, controlling means for causing the reference image and the ultrasonic image to be displayed on a screen, and displaying means for displaying the reference image and the ultrasonic image, wherein, in accordance with the tomographic image data and a positional relationship between the ultrasonic probe and a patient, the reference-image generating means extracts tomographic image data of a portion corresponding to a view area of the ultrasonic image to generate the reference image.