1. A medical image processing apparatus, comprising: a branch structure extraction means for extracting a branch structure from a three-dimensional medical image representing a subject's internal structure having the branch structure and a surrounding structure which is a structure located around and functionally associated with the branch structure; a surrounding structure area extraction means for extracting a surrounding structure area which includes the surrounding structure from the three-dimensional medical image; an attention branch structure setting means for setting an attention branch structure which is an attention portion of the branch structure; an attention surrounding structure area estimation means for estimating an attention surrounding structure area functionally associated with the attention branch structure from the surrounding structure area based on the branch structure; an evaluation value obtaining means for obtaining an evaluation value of function and/or morphology of the subject's internal structure in the estimated attention surrounding structure area; and a mapped image generation means for generating a mapped image which is an image generated by mapping the evaluation value in the attention surrounding structure area to a morphological image generated from the three-dimensional medical image and representing morphology of at least one of the attention branch structure and the attention surrounding structure area.