PURPOSE: To enable the H/V difference caused by the property of the deflection york of a dot-inline tube to be corrected with a preferred tendency by installing a lamp mask apart from a light source, and giving an anisotropy to the position of the light source due to the relationship between the light source and the lamp mask.

CONSTITUTION: When a part of a panel for a color picture tube is exposed to light irradiated from a direction (V) with a deflection angle of, for example, ω, the center (O) of an arc source 11 becomes the imaginary light source. On the other hand, when a part of the panel is exposed to light irradiated from a direction (H) with a deflection angle of ω, a lamp mask 10 doesn't seem to emit light from the center (O) of the arc source 11, and light seems to be discharged from the point indicated by a mark (X) which is apart from the point (O) by Δ. Consequently, the conventional tendency of being hardly corrected with a correction lens can be rectified by devising both the shape of the light source, and the lamp mask provided over the light source.