PURPOSE: To obtain a uniform luminous length of ≥220mm with fluorescent discharge lamp length of ≤240mm including projected parts of electrodes by making the width of a third electrode installed linearly in tube wall in longitudinal axis direction wide in the central part and narrow in both end parts.

CONSTITUTION: In a cold cathode fluorescent discharge tube, comprised of a phosphor applied to a part or the whole part of tube wall of a transparent tube, a rare gas filled in the tube, and electrodes in both ends of the tube, the width of a third electrode installed linearly in the tube wall in longitudinal axis direction is so made as to be relatively wide in the central part and narrow in both end parts. For example, in the case that the width in the center is 1, that in the both end parts is 1/5-1/2, preferably 1/4-1/3. With the width of the third electrode in the central part of 210mm being made 3mm and 1mm width in both end parts of 15mm, uniform luminous length of ≥220mm with fluorescent discharge lamp length of ≤240mm is achieved.