PURPOSE: To perform an easy work of correction for an off-center of deflection of electron beams in a single-beam cathode-ray tube, by arranging a ring magnet not magnetized in a base of the cathode-ray tube, magnetizing it from the outside and performing a correction of the electron beam.

CONSTITUTION: A ring magnet 10 before its magnetization is arranged in a cathod-ray tube base 9 in such a manner that the axis of the ring is aligned to the tube axis, after a completion of mounting said base 9 to a cathode-ray tube 1, magnetized from the outside to perform the correcting work of an electron beam. The magnetization of the ring magnet 10 is performed by such a method, for instance, that an electromagnetic coil 11 having a core 12 is symmetrically arranged to the axis on the periphery of the base 9 to flow an electric current through the coil 11. Then an intensity of magnetization is adjusted by the current passing through the coil 11 while its polarity is controlled by turning the coil 11 and the core 12. In this way, a double work of preliminary and final base mounting can be eliminated to simplify the work, thus a misalignment of the correction can be prevented.