PURPOSE: To enable the alignment adjustment to be performed accurately and easily by making a cathode-ray tube to project a dot-like pattern through a raster scanning, feeding a focus current to a focus-magnetic-field adjusting coil, and adjusting the level of the direct current.

CONSTITUTION: A focus magnet 1 is attached over a neck 21 of a cathode-ray tube 2. Next, the tube 2 projects an image pattern as illustrated in the figure (A) by receiving a raster scanning. After that, a current as indicated in the figure (B) is fed to the coil of the magnet 1, and a direct-curent level (ΔIF1) is adjusted so that a dot-like pattern 51 becomes a most clear point. At this point, as illustrated in the figure (C), the dot-like pattern 51 consists of a most intensively focused point 51a and an unfocused point 51b located apart from one another. The above adjustment is carried out with a bipolar magnet 4 so that the points 51a and 51b have the same center.