1. An ultrasonic diagnosis apparatus comprising: an ultrasonic image generating unit configured to generate an ultrasonic tomographic image on a scan plane of an ultrasonic wave from reflection echo signals output from an ultrasonic probe; a storage unit configured to store volume image data pre-obtained by a diagnostic imaging apparatus; a reference-image generating unit configured to extract reference tomographic image data corresponding to the ultrasonic tomographic image from the volume image data stored in the storage unit and generate a tomographic reference image; a cine-memory configured to store the ultrasonic tomographic image generated by the ultrasonic-image generating unit; a position sensor configured to detect a position and an inclination of the ultrasonic probe; a coordinate determining unit configured to determine scan-plane-coordinate data of the ultrasonic tomographic image in accordance with an output from the position sensor; a scan-plane-coordinate-system storing unit configured to store the determined scan-plane-coordinate data; a controller configured to cause the tomographic reference image and the ultrasonic tomographic image to be displayed on a screen; and a display unit configured to display the reference image and the ultrasonic tomographic image; wherein: an image processing unit reads the ultrasonic tomographic image from the cine-memory and causes the reference tomographic image corresponding to the read ultrasonic tomographic image to be displayed, the reference image being output from the reference-image generating unit, cine playback of the ultrasound tomographic image is executed by referring to ultrasonic tomographic image data stored in the cine-memory, and cine playback of the reference tomographic image is executed by using the scan-plane coordinate data stored in the scan-plane-coordinate storing unit, and the ultrasonic tomographic image data and the scan-plane coordinate data are stored in synchronization with each other.