Provided is a battery pack that can securely prevent liquid, such as water and wash fluid, attached to an outer surface of a packaging case housing a plurality of electric cells from entering an internal space of the packaging case from between a tray and a cover and that also allows easily performing attachment and detachment work of the cover to and from the tray. The packaging case includes an edge cover for covering the whole circumference of a lower flange portion of the tray and an upper flange portion of the cover that abut each other. The edge cover includes a first section facing the lower flange portion, a second section facing the upper flange portion, and a connecting portion for connecting base ends of the first section and the second section. A plurality of female threaded portions are arranged on either the first section or the second section. Screw insertion holes for causing male screw members to be inserted according to the arrangement of the female threaded portions are arranged on either the first section or the second section in which the female threaded portions are not arranged, on the lower flange portion, and on the upper flange portion.