Magnetic leakage fields occur in CRT's with magnetic deflection of the electron beam. These fields extend outside the deflection zone and can reach a person in the vicinity of the CRT. The magnetic leakage fields are considered to cause injuries by reason of the electric currents induced in the body cells. The current strength is proportional to the time change in the magnetic field, and relatively large currents are obtained in the cells, e.g. from the return pulse of the scanning line sweep in the CRT. In a known solution for reducing the magnetic field in front of the CRT, a flat short-circuited loop has been placed horisontally above the CRT so that the leakage field is deflected obliquely upwards. This measure is simple, but has a limited field of use, since the field does not decrease but is only given another direction. It has also been proposed to screen the CRT with a casing of magnetic material. The casing cannot cover the display surface of the CRT and gives no reduction of the leakage field in front of it.