In the present invention, a backlight (3) serving as a planar light source unit is equipped with: multiple LEDs (12); and a bottom plate (11a) having a mounting surface (11a1). The multiple LEDs (12) are two-dimensionally arranged on the mounting surface (11a1) within a rectangular area (RA) that is smaller than the bottom plate (11a). In addition, the arrangement density of the LEDs in the rectangular area (RA) is lower at the center part (Rc) than at the peripheral part (Rp). The rectangular area (RA) has a corner area, where at least one LED (12) is provided, at each of the four corners thereof. The LEDs (12) positioned in the respective corner areas are installed such that the central axes of the LEDs lean toward the periphery side of the rectangular area (RA) with respect to the direction perpendicular to the mounting surface (11a1).