1. A medical image processing device comprising: an input section to which a biological mucous membrane image obtained by picking up an image of a biological mucous membrane is inputted; a region extracting section that extracts a mucous membrane microstructure region corresponding to a mucous membrane microstructure, which is a microscopic structure included in the biological mucous membrane, from the biological mucous membrane image inputted to the input section; a closed region identifying section that identifies at least one closed region regarded as being surrounded by the mucous membrane microstructure region; and a unit region setting section that sets a unit region, which is a region set as one unit in terms of biological histology, on the basis of the mucous membrane microstructure region extracted by the region extracting section and the closed region identified by the closed region identifying section.