PROBLEM TO BE SOLVED: To provide a highly versatile medical image generation processing device and a program, capable of highly reproducibly and appropriately specifying a voxel group constituting a region of interest in a medical image space.SOLUTION: A medical image generation processing device includes: a reference voxel setting part 121 for setting a reference voxel belonging to a region of interest in a voxel space a CT value range setting part 122 for setting a range of numerical values for extracting a region of interest including CT values carried by the reference voxel a combined voxel group specifying part 123 for specifying a combined voxel group composed of a group of voxels which carry CT values in the range of numerical values for extracting the region of interest in the voxel space and which are spatially combined with the reference voxel and a correlation computing part 13 for obtaining correlations between a boundary value and a volume value of voxels constituting the combined voxel group when the boundary value in the range of numerical values for extracting the region of interest is changed.
