A flame due to abnormality is prevented from leaking to an outside. A battery pack includes a first inorganic plate disposed at an opening of a housing and spaced apart from a battery holder by a first gap (d1), and a second inorganic plate spaced apart from the first inorganic plate by a second gap (d2). The first inorganic plate has first through-holes opened in a predetermined first pattern. The second inorganic plate has second through-holes opened in a prescribed second pattern. The housing includes an inner rib projecting from an inner surface of the opening of the housing. The inner rib is provided between the first and second inorganic plates to form the second gap (d2). The first and second inorganic plates are positioned such that the second through-holes are deviated from the first through-holes to prevent an inside of the housing from being viewed from an outside of the housing through the second through-holes.