A planar light source includes a mounting substrate, a plurality of light sources, a partition member, a frame body, a wavelength conversion member, and a light diffusion plate. The light sources are arranged two-dimensionally on the mounting substrate in a plan view. The partition member includes a wall portion surrounding each of the light sources except for outermost ones of the light sources in the plan view. The wall portions are located inward of the outermost ones of the light sources. The frame body has a bottom portion and a lateral wall surrounding the mounting substrate. The wavelength conversion member is disposed on the lateral wall of the frame body. The light diffusion plate is disposed above the plurality of light sources and the wavelength conversion member.