A morphology image representing the morphology of a specific organ including a tubular structure in the inside thereof and a function image representing a function level at each position in the organ are obtained. A structure region representing a structure dominating the organ is extracted from the morphology image. A specific partial region in the extracted structure region and a dominated region in the organ are determined, and the dominated region being dominated by a structure in the partial region. In that case, at least one of the partial region determination step and the dominated region determination step is performed by using the function image.
