A battery charger on which power conversion components for converting commercial power to direct current power are mounted, includes a core frame formed into a C-letter shape in horizontal cross section. The components at least producing heat among the power conversion components are mounted on one side confined by a C-letter cross section of its both sides. An outer housing is attached to the core frame so as to cover the core frame, and a fan supplies cooling air to a region confined by the C-letter shaped cross section of the core frame.