A normal lower jaw position of an examinee is determined. A lower jaw position determining method for determining a normal lower jaw position of an examinee, includes: center calculating for obtaining measurement data by measuring movement of a head of the examinee, and calculating a center of movement resulting from approximating the movement of the head as rotational movement of a rigid body; lower jaw orbit measuring for measuring a plurality of orbits of masticatory movement of the lower jaw, for a plurality of lower jaw positions of the examinee; and position determining for (i) approximating the masticatory movement of the lower jaw as rotational movement of a rigid body to find one of the plurality of measured orbits of the lower jaw whose center of movement in the approximation matches the calculated center of movement of the head, (ii) determining a lower jaw position that corresponds to the found orbit of the lower jaw to be a normal lower jaw position for the examinee, and (iii) outputting the determined normal lower jaw position.