The present invention provides a battery pack mounted to a battery pack mounting part of a device for supplying power, including: a base plate including one surface on which two or more battery module assemblies respectively having a plurality of battery cells arranged therein are mounted in a separated state from each other with a predetermined interval therebetween; a cover member mounted on one surface of the base plate while enclosing the battery module assemblies; and a reinforcement supporting member positioned at a separation part between the battery module assemblies while supporting the mounting state of the cover member for the base plate, wherein the battery pack is mounted in a state in which an external circumferential surface of the cover member faces a battery pack mounting part of a device.