A cooling apparatus comprising a liquid immersion cooling apparatus filled with liquid coolant, the cooling apparatus including an electronic device (100; 300) that is immersed in the liquid coolant filled in the liquid immersion cooling apparatus (352, 452, 452a, 452b, 552, 552a, 552b), and directly cooled, the electronic device being configured to be housed in a housing part of the liquid immersion cooling apparatus, the electronic device comprising: a base board (110; 310); a plurality of storage substrates to be arranged on at least one surface of the base board (110; 310); a backplane including a plurality of connectors for electric connection of the respective storage substrates (351, 451, 551), the backplane being mounted orthogonally onto the at least one surface of the base board (110; 310); and a plurality of flash storage units (352, 452, 452a, 452b, 552, 552a, 552b)mounted on the respective storage substrates (351, 451, 551), wherein: the backplane includes a combination of a plurality of backplane units (340a, 340b) arranged in a length direction of the base board (110; 310) to form a single substrate, each of the backplane units (340a, 340b) including a signal connector (3311a, 3311b) and a power connector (3312a, 3312b), the signal connector and the power connector being disposed separately for each of the backplane units (340a, 340b), and the flash storage units (352, 452, 452a, 452b, 552, 552a, 552b) each having a rectangular shape are arranged on a surface parallel to at least one surface of each of the storage substrates (351, 451, 551) so as to be adjacent one another in a width or a length direction, or in both the width and the length directions of the rectangular-shaped flash storage unit (352, 452, 452a, 452b, 552, 552a, 552b). a base board (110; 310); a plurality of storage substrates to be arranged on at least one surface of the base board (110; 310); a backplane including a plurality of connectors for electric connection of the respective storage substrates (351, 451, 551), the backplane being mounted orthogonally onto the at least one surface of the base board (110; 310); and a plurality of flash storage units (352, 452, 452a, 452b, 552, 552a, 552b)mounted on the respective storage substrates (351, 451, 551), wherein: the backplane includes a combination of a plurality of backplane units (340a, 340b) arranged in a length direction of the base board (110; 310) to form a single substrate, each of the backplane units (340a, 340b) including a signal connector (3311a, 3311b) and a power connector (3312a, 3312b), the signal connector and the power connector being disposed separately for each of the backplane units (340a, 340b), and the flash storage units (352, 452, 452a, 452b, 552, 552a, 552b) each having a rectangular shape are arranged on a surface parallel to at least one surface of each of the storage substrates (351, 451, 551) so as to be adjacent one another in a width or a length direction, or in both the width and the length directions of the rectangular-shaped flash storage unit (352, 452, 452a, 452b, 552, 552a, 552b). the backplane includes a combination of a plurality of backplane units (340a, 340b) arranged in a length direction of the base board (110; 310) to form a single substrate, each of the backplane units (340a, 340b) including a signal connector (3311a, 3311b) and a power connector (3312a, 3312b), the signal connector and the power connector being disposed separately for each of the backplane units (340a, 340b), and the flash storage units (352, 452, 452a, 452b, 552, 552a, 552b) each having a rectangular shape are arranged on a surface parallel to at least one surface of each of the storage substrates (351, 451, 551) so as to be adjacent one another in a width or a length direction, or in both the width and the length directions of the rectangular-shaped flash storage unit (352, 452, 452a, 452b, 552, 552a, 552b).