To accurately perform the centering of a nipple and a grease receiving port by moving a main body so that the nipple abuts on the grease receiving port of a mandrel.

At the time of connecting a grease supplying device 8 and a mandrel shaft to each other, an actuator is operated, and when a main body 13 is moved to a mandrel shaft side through a fitting material 16, a nipple 10 is moved together, and a tip of the nipple 10 is inserted into a grease receiving port 15 of the mandrel shaft so as to connect the both to each other. At this stage, in the case where the tip of the nipple 10 and the center line of the grease receiving port 15 are displaced from each other, or in the case where the relative oscillation is generated between the both, a spherical base part 10a of the nipple 10, which is supported by a spherical seat 11a of a bearing part 11, is freely turned a little so as to perform the accurate centering.