A light-emitting element unit which can improve color purity of light emitted from a color filter is provided. A display device with high color purity and high color reproducibility is provided. The light-emitting element unit includes a wiring board, a light-emitting element chip provided over the wiring board, a micro optical resonator provided over the wiring board and at the periphery of the light-emitting element chip, and a phosphor layer covering the light-emitting element chip and the micro optical resonator. The display device includes a display panel having a coloring layer and a backlight module having the light-emitting element unit. Examples of the display panel include: a liquid crystal panel; and a display panel including an opening portion provided over a first substrate, MEMS moving over the opening portion in the lateral direction, and a second substrate provided with a coloring layer in a portion corresponding to the opening portion.