A simple and compact joint coupling for a prosthetic brace can maintain an integrally fixed state, adapt for a movable region training and a movable state, and has a small dividing of a bending angle. The rotor having a recessed groove formed is rotatably intruded into a first coupling base, and protruding pieces and provided on the circumferential surface of a second coupling base are fitted to the recessed groove. In addition, the surface of the second coupling base is covered with an operation cover for operating an operation pin. A first coupling base and the second coupling base are pivoted so as to be rotated by a central shaft and a stopper screw for preventing the fall off of the central shaft. The circumference of the recessed groove for arraying and charging the spheres is bisected by convex parts and. Spheres are arrayed and charged in the recessed groove of one bisected half, and a freely expansible and contractible spring is attached to the recessed groove of the other half.