A mounting disk 60 for a mandible die comprises an upper rotary plate 61 and a lower rotary plate 62. At their extremities, the two plates are rotatably fastened to each other by means of a pivot member 64. If the median points are offset, then the entire mounting disk 60 is turned around a rotational axis provided by a vertical rotary shaft 3 which is fitted to a base of an articulator screwed into a threaded hole 74, to thereby achieve a median registration. If molars are positionally offset in spite of the coincident medial points, then a locking rode 81 is loosened so that the upper rotary plate 61 can turn around a rotational axis defined by the pivot member 64 till the molars come into registration, after which the plates are firmly fixed by the locking rod 81. The angle of rotation at that time is read by use of a scale 76 formed on an arcuate surface 67. More precise fundamental data can thus be obtained for the jaw joint positional coordination.