PURPOSE: To prevent the distortion of image screen even though a temperature variation occurs, by composing a raster distortion correcting magnet unit with the first and the second magnets of a rotary adjusting type superposing in the reverse polarities each other.

CONSTITUTION: The first and the second magnets 5 and 6 are superposed to be in the reverse polarities each other, and held rotatable by a pair of magnet holders 3 and 3. By the rotation adjustment of the first magnet 5, the raster shown in the one point chain line is corrected to push in as the dotted line, and after that, the first magnet 5 is fixed to the magnet holders 3 and 3. Then, the second magnet 6 is installed to the magnet holders 3 to be in the reverse polarity. And by the rotation adjustment of the second magnet 6, the raster in the dotted line is corrected to the raster in the solid line by pulling out 5 parts, about a half of the pushing-in amount by the first magnet 5 whose amount is 10 parts. Therefore, the raster does not move even if a temperature variation occurs, and the adequate position initially adjusted can be maintained.