A power supply device 1 includes a main circuit board 20, a power component 22 connected to the main circuit board 20, a filter component 24 connected to the main circuit board 20, and a casing 10 which houses the main circuit board 20, the power component 22, and the filter component 24. The casing 10 includes a base plate 11 which includes a flat surface 11a in which a fin 14 for heat dissipation is provided on a bottom-surface side, and a protruding part 15 which protrudes from the flat surface toward the fin. The power component 22 and the main circuit board 20 are placed on the flat surface, and the filter component 24 is housed in the protruding part 15.