An ultrasonic diagnosis apparatus comprising: an ultrasonic image generating unit for generating an ultrasonic image based on reflection echo signals output from an ultrasonic probe; a storing unit for storing volume image data pre-obtained by a diagnostic imaging apparatus; a reference-image generating unit for extracting tomographic image data corresponding to the ultrasonic image from the volume image data stored in the storing unit and reconstructing a reference image; a first reference-point setting unit for setting a first reference point on a distinctive point of the reference image displayed on a displaying unit, so that the first reference point is set on a body surface or inside the body of the object; characterised by: a source for forming a reference coordinate system by generating magnetism or light in a space including an object; a position sensor attached to the ultrasonic probe for detecting a position and an inclination of the ultrasonic probe using the magnetism or light generated by the source; a second reference-point setting unit for setting a second reference point on the distinctive point of the ultrasonic image displayed on the displaying unit by locating the ultrasonic probe with the position sensor at a position corresponding to the first reference point in case the first reference point is set on the body surface of the object, or by using a pointing device such as a mouse in case the first reference point is set inside the body of the object; and a coordinate determining unit for determining coordinates of the reference image associated with coordinates of a scan plane of the ultrasonic image in accordance with the first reference point, the second reference point, and the position and the inclination of the ultrasonic probe detected by the position sensor, wherein the source is set so that the reference coordinate system and the coordinate system of the volume image data are substantially parallel to each other, and wherein the reference-image generating unit is adapted to generate the reference image by associating a coordinate system of the volume image data with a coordinate system of the scan plane of the ultrasonic image based on the coordinates determined by the coordinate determining unit. an ultrasonic image generating unit for generating an ultrasonic image based on reflection echo signals output from an ultrasonic probe; a storing unit for storing volume image data pre-obtained by a diagnostic imaging apparatus; a reference-image generating unit for extracting tomographic image data corresponding to the ultrasonic image from the volume image data stored in the storing unit and reconstructing a reference image; a first reference-point setting unit for setting a first reference point on a distinctive point of the reference image displayed on a displaying unit, so that the first reference point is set on a body surface or inside the body of the object; a source for forming a reference coordinate system by generating magnetism or light in a space including an object; a position sensor attached to the ultrasonic probe for detecting a position and an inclination of the ultrasonic probe using the magnetism or light generated by the source; a second reference-point setting unit for setting a second reference point on the distinctive point of the ultrasonic image displayed on the displaying unit by locating the ultrasonic probe with the position sensor at a position corresponding to the first reference point in case the first reference point is set on the body surface of the object, or by using a pointing device such as a mouse in case the first reference point is set inside the body of the object; and a coordinate determining unit for determining coordinates of the reference image associated with coordinates of a scan plane of the ultrasonic image in accordance with the first reference point, the second reference point, and the position and the inclination of the ultrasonic probe detected by the position sensor,