PURPOSE: To prevent the strength of the light discharged through a slit section from being dispersed in the axial direction by making the width of an outer electrode smaller than the width of the slit section of a light shielding film.

CONSTITUTION: The width W1 of an outer electrode 5 is made smaller than the opening width W2 of a slit section 7 formed with a light shielding film 6. According to this constitution, a positive column A is pulled toward the outer electrode 5 side to approach a tube wall during lighting, hut the width of the outer electrode 5 is formed small, thus the meandering width of the positive column A is made small. As a result, the positive column A is prevented from being largely protruded from the width of the slit section 7. Accordingly, a phosphor film 2 positively facing the slit section 7 is strongly illuminated, thus strong emission is discharged nearly uniformly along the axial direction, and the dispersion of light distribution characteristic in the axial direction can be dissolved.