To provide a side-light type planar lighting device capable of arranging more LEDs at a side face section of a light guide plate.

The planar lighting device 10 has the light guide plate 11, wherein recessed sections 12 and projected sections 13 are formed alternately and repeatedly along one side-face section, and the LEDs 21 made of first-train LEDs 21a and second-train LEDs 21b which are respectively arranged on the recessed sections 12 and the projected sections 13. The projected sections 13 are formed of parallel sections 14 having an approximately constant width, and an expanding section 15, wherein its width is spread out as it is separated from the parallel section 14. The width W2 of a top face 13a of the projected section 13 is set larger than an opening width W3 of each second-train LED 21b and larger than a width W4, in a longitudinal direction of a lamp house 23. Furthermore, the lamp house 23 of each second-train LED 21b is arranged so as to partially overlap with that of the adjacent first train LED 21a, when viewed projecting in a light guide plate 11 direction.