In a phase unwrapping evolution method according to the invention, steps of grouping phase data first, phase unwrapping evolution targeting groups is performed, and, then, merging of the target groups is performed are repeatedly applied. As unwrapping evolution processing proceeds, groups increase and information on a phase difference among the group increases. Thus, the influence of phase data that tends to be a cause of failure of unwrapping evolution gradually decreases and a result with higher robustness than the conventional method is obtained. In addition, a group once subjected to unwrapping evolution continues to be subjected to unwrapping evolution as a new group created by merging. Thus, even if a phase is decided once, the group is subjected to wrapping evolution many times in order to match the phase with phases of other groups. As a result, it is possible to prevent a series of occurrence of failure of unwrapping evolution. Failure of unwrapping evolution is reduced compared with the conventional method and stability of unwrapping evolution is improved.