A cooling apparatus including an electronic device (100; 300) that is immersed in a liquid coolant filled in the cooling apparatus, and directly cooled, the electronic device (100; 300) being configured to be housed in a housing part of the cooling apparatus, the electronic device (100; 300) comprising: a base board (110; 310); a plurality of storage substrates (351; 451; 551) 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 (351; 451; 551) substrates, 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 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); characterized in that the base board (110; 310) includes a primary member and a secondary member; the primary member includes a plurality of cuts each formed in a width direction for fixing a plurality of support plates(315, 316) each having grooves that support the storage substrates (351; 451; 551) to the primary member; the secondary member includes a plurality of pawls which are inserted into a plurality of slits formed in the backplane, respectively, and fixed to the primary member; and the support plates (315, 316) include holes for passage of the liquid coolant. a base board (110; 310); a plurality of storage substrates (351; 451; 551) 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 (351; 451; 551) substrates, 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 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 primary member includes a plurality of cuts each formed in a width direction for fixing a plurality of support plates(315, 316) each having grooves that support the storage substrates (351; 451; 551) to the primary member; the secondary member includes a plurality of pawls which are inserted into a plurality of slits formed in the backplane, respectively, and fixed to the primary member; and the support plates (315, 316) include holes for passage of the liquid coolant.