PURPOSE: To minimize the amount of change in the inductance of a dynamic coil by using a plastic magnet, to provide a clear image by forming a beam spot into almost perfect circle even when a glass bulb is enlarged, and to reduce the cost by storing the device in a limited space in a compact way.

CONSTITUTION: The entire circumference of an annular electron lens 2 installed in a glass bulb neck 1 in which an electron beam E passes through a tube, is formed into double-layered structure of an inner layer part A and an outer layer part B. Either a coil or a permanent magnet is installed in the inner layer part A or in the outer layer part B so that each of them is divided into two parts in the front and the rear sides. A D.C. current is flown in either the front or rear side of the coil, and a metallic magnet 5 is installed in the side of this D.C. coil 4a, while a high frequency A.C. current up to approximate 100KHz is flown in the other side of the coil, and a plastic magnet 6 is installed in the side of this A.C. coil 4b.