To generate three-dimensional tomogram, when displaying to superimpose a three-dimensional elastic image on a three-dimensional tomogram, allowing an operator to intuitively recognize the shape and the volume of a hard portion or a soft portion existing in biomedical tissue in a region of interest.

An elastic image volume rendering means 66 has an opacity table setting opacities corresponding to elasticity values of voxels of elastic volume data 62, and cumulatively adds the opacities by multiplying each of luminance values of the respective voxels of the tomographic volume data aligned along the line of sight by an opacity corresponding to each elasticity value of each of the voxels of the elastic image volume data which the voxel correspond to. Then, a residue obtained by subtracting the cumulative value of the opacity till immediately before the voxel from the upper limit threshold of a preset opacity, is multiplied by the opacity of the present voxel, and the opacities of the voxels are cumulatively added to be defined as a pixel value of the three-dimensional gray-scale tomogram.