Abstract: A cathode ray tube (3) (CRT) has a deflecting coil (1) surrounded by a funnel-like casing (4) of magnetic material. The deflecting coil generates a magnetic deflecting field (B) for the electron beam and a magnetic leakage field (BL) in the CRT environment. The leakage field is composed of a dipole field and a quadrupole field. To reduce the magnetic field strength in the CRT environment a magnetic compensation field which is counterdirected to the leakage field is generated. The compensation field is composed of a dipole field which is generated by a first compensation loop (7) and a quadrupole field which is generated by a second compensation loop (9). The first compensation loop (7) is substantially flat and at right angles to the magnetic deflecting field (B). The second compensation loop (9) is flat and at right angles to the longitudinal symmetrical axis (z) of the CRT and has an upper (9a) and a lower (9b) part which generate two mutually opposing dipole fields (DK2,DK3).