A fitting device for an ornamental accessory is made up of a pair of connecting members each having a cylindrical portion on an end to be fitted together in a rotatable manner relative to each other. One of the connecting members has at its fitting end at least one piece of guide grooves formed in series. The guide groove is made up of a thrust groove which is open into an outside and extends in an axial direction of the connecting member, a rotation groove which bends from an inner end of the thrust groove and extends in a circumferential direction, and a fixing groove which bends from that end of the rotation groove which is away from the thrust groove towards the fitting end. The other of the connecting members has at its fitting end a projection which is thrusted into the thrust groove and moves along the rotation groove. The projection is positioned to correspond to the guide groove. Each of the connecting members has inside its fitting end portion magnet pieces disposed on a plane. The magnet pieces have N pole and S pole arranged to lie alternately in a circumferential direction to form magnetized surfaces facing outwards.