A shape data generation method relating to this invention includes: first generating first three-dimensional voxel data that represents a target obj ect by using first tomographic images, in which a first region occupied by the target object is designated, among plural tomographic images; extracting, from the first tomographic images, brightness values of voxels included in the first region; second generating a function for calculating a probability that a voxel is included in the first region by using the extracted brightness values; calculating, for each voxel among voxels in a voxel space that includes the plural tomographic images, a probability by using a brightness value of the voxel and the function; and third generating second three-dimensional voxel data that represents the target object by using the first three-dimensional voxel data and probabilities calculated for the voxels in the voxel space.