An oral-area positioning device is provided in the invention. The oral-area positioning device includes a storage circuit, a positioning circuit and a calculation circuit. The storage circuit stores information corresponding to a plurality of oral areas. The positioning circuit obtains a target image from an oral-image extracting device, and obtains a first position estimation result according to the information corresponding to the plurality of oral areas and a first algorithm. The positioning device obtains a second position estimation result at least according to the information corresponding to the plurality of oral areas, a second algorithm and a reference image position of a reference image, wherein the reference image position is one of the oral areas. The calculation circuit generates a third position estimation result according to the first position estimation result and the second position estimation result.