PURPOSE: To correct effectively unbalance of a rotator by preventing the fragment from the surface of the rotator from attaching at the laser photosystem by applying laser beams from the slanted directions of the applying surface of the rotator.

CONSTITUTION: Laser beam 3A from a laser generating device 2 is applied in the surface straight to the rotational axis of a rotator 1 from the slanted direction of the irradiated surface of the rotator 1. A fragment from the surface of the rotator 1 scatters in the direction of an arrow 6A which is different direction from a protection glass 5. Thus it is prevented that the fragment attaches to the glass 5 and lowers projection rate of the laser 3A. Also, laser beam 3B is applied at a spot of the rotator 1, and the laser beam 3B is applied later at the spot a little apart from the former applied spot in the direction of the axis of the rotator 1. In this case, a fused part does not remain between these applied spots of laser on the surface of the rotator 1, and the amount of unbalance of the rotator 1 can be removed effectively.