Backlight device and display apparatus

A backlight device comprising:

• a substrate having a principal surface;
• a plurality of light-emitting elements, supported by the principal surface of the substrate, that emit excitation light;
• a first phosphor layer containing a phosphor that produces fluorescence upon receiving the excitation light;
• and a partitioning member forming a plurality of spaces each of which accommodates any one or more of the plurality of light-emitting elements between the principal surface of the substrate and the first phosphor layer, wherein the partitioning member includes a plurality of walls each of which, in a top view, encloses the one or more of the plurality of light-emitting elements accommodated separately in each of the plurality of
• spaces, a plurality of apices each of which connects ones of the plurality of walls that are adjacent to each other, one or more first through-holes formed in the plurality of walls, and one or more second through-holes formed in the plurality of apices, an air gap is formed between adjacent two walls of the plurality of walls by the two walls and one of the apices that connects the two walls, and a second through-hole formed in the one of the apices among the one or more second through-holes communicates with a first through-hole formed in one of the two walls among the one or more first through-holes via the air gap.