Planar lighting device and mounting substrate including conduction pattern with extension parts

A planar lighting device comprises: a mounting substrate having a conduction pattern having an extension part formed on a base material, and a cover member is arranged on the conduction pattern, wherein the cover member has an opening that exposes together the two lands of the two adjacent light sources, and wherein the extension parts comprise: a first extension part formed to extend from a first end portion of the lands toward the light guide plate and to extend under the cover member; a second extension part formed to extend from a second end portion, toward the light guide plate and the other land of the pair of the lands and to extend under the cover member; and a third extension part formed to extend from the first end portion, toward an opposite side to the light guide plate and to extend under the cover member.