PURPOSE: To keep a uniform focusing quality all over a screen and obtain a cathode ray tube having remarkably improved resolution by regulating color purity of the whole screen using the first and the second magnets for regulating color purity.

CONSTITUTION: The second color purity correction magnet 100 is arranged near an outlet of the final electrode 24 of an in-line en bloc electron gun to regulate power purity. An electron beam is to pass an electron gun central axis D-G in order to evenly disperse halo components on the whole screen. Accordingly the electron beam passing D-G axis in Fig. is to correct its track from the point E far from the main lens with the second color purity correction magnet so that it may pass the central exposure point C of the cathode ray tube whose color purity on the screen is to be corrected. That is to say that the final electron beam track is to be D-E-C-A. Consequently the whole screen has uniform focusing quality and the resolution quality improves remarkably.