To provide a planar light source device capable of mitigating luminance irregularity due to presence of a barrier rib; and a liquid crystal display device assembly.

This liquid crystal display device assembly is provided with: a transmission type liquid crystal display device 10 having a display region composed of pixels arranged in a two-dimensional matrix-like form; and this planar light source device 40 illuminating the liquid crystal display device 10 from the back. The planar light source device 40 comprises PQ planar light source units 41 corresponding to PQ display region units 12 when it is assumed the display region of the liquid crystal display device 10 is divided into the PQ virtual display region units 12, and is characterized in that each planar light source unit 41 is isolated from another planar light source unit 41 by a plate-like barrier rib 43; and, when it is assumed that the height direction of the barrier rib 43 is a Z-direction, the cross section of the barrier rib is an undulating line shape when the liquid crystal display device 10 side of the barrier rib 43 is cut by a plane orthogonal to the Z-direction.