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, wherein the mapped image is an image generated by mapping the evaluation value in the attention surrounding structure area to a broad morphological image representing morphology of an area of the subject's internal structure which includes, as a part, the attention branch structure and the attention surrounding structure area, the image being generated by mapping each evaluation value to an area of the broad morphological image corresponding to the area where each evaluation value is obtained by the evaluation value obtaining means, in which a boundary between the attention surrounding structure area and a surrounding structure area other than the attention surrounding structure area is distinguishable, and the evaluation value obtaining means is a means that obtains an evaluation value for each sub-area constituting an area of the subject's internal structure which includes, as a part, the attention surrounding structure area.