PURPOSE: To perform the operation of each adjusting magnet easily and reliably and facilitate the lock action of a lock ring by providing a male screw for being screwed to the lock ring at one end of a magnet holder and multiple notches in the axial direction and a groove surrounding the outer surface of a holder cylinder at the other end.

CONSTITUTION: A peripheral direction groove 6a with which the inner edge of a stop ring is coupled, axial direction notches 6b, and a male screw 6c being screwed to a lock ring are provided on a magnet holder 6. First, the lock ring 7 is screwed to the magnet holder 6, next a static convergence adjusting magnet 8 is inserted (either six-poles or four-poles can be inserted first), furthermore a color purity adjusting magnet 10 is inserted, and finally the inner edge of the stop ring 13 is coupled with the groove 6a surrounding the outer surface of a magnet holder end cylinder so as to serve as a stopper.