PURPOSE: To enable a highly efficient break-in rotation by making a ball bearing simple substance a break-in rotation while applying a pre-load to one side race with the pressure spring of a fixed support part and applying rotation drive force to the other race.

CONSTITUTION: A ball bearing 23 is assembled by previously sticking a solid lubricant to many balls 23c and inserting them between an inner race 23a and an outer race 23b, and mounted between the rotation support part 35 of a break-in rotation device. Then the device is rotated on a given number of revolution program with a rotation controller. A pre-load force produced by the disc spring provided to the part 35 is applied to the race 23b on a given pre-load program. When a break-in rotation is finished in this way, the bearing is removed from the device, made ultrasonic cleaning, and assembled to the rotation mechanism part of a rotating anode type X-ray tube. This enables a highly efficient break-in rotation.