A planar light source includes a substrate, a reflective member having a plurality of openings and at least one slit, and a light source disposed in each of the openings. The plurality of openings are arranged in m rows along a first direction and in n columns along a second direction that intersects the first direction. The at least one slit includes at least one first slit arranged in a first region and intersecting a first virtual straight line at a prescribed position in the first region. The first virtual straight line is parallel to the first direction. The first region is located between one or more openings in a kth row (k is an integer equal to or greater than 1 and less than or equal to m−1) and one or more openings in a (k+1)th row and extends in the first direction.