A battery pack comprising: (a) a battery module array comprising battery modules configured to have a structure in which battery cells or unit modules, each of which has two or more battery cells mounted therein, are stacked in an inverted state, the battery modules being arranged in two or more rows; (b) a pair of side support members (a front support member and a rear support member) configured to respectively support a front and a rear of the battery module array in a state in which the side support members are in tight contact with outermost battery modules of the battery module array; (c) lower end support members coupled to lower ends of the side support members to support a lower end of the battery module array; (d) two or more first upper mounting members coupled to upper ends of the side support members and to lower ends of the inverted battery modules, one end of each of the first upper mounting members being fastened to an external device; (e) a second upper mounting member configured to vertically intersect the first upper mounting members, the second upper mounting member being coupled to upper ends of the first upper mounting members, opposite ends of the second upper mounting member being fastened to the external device; and (f) a rear mounting member located at a rear of the battery module array, opposite ends of the rear mounting member being fastened to the external device, wherein at least one of the side support members is partially provided with a weak portion exhibiting low resistance to volume expansion to induce local deformation of the battery modules upon occurrence of swelling, thereby achieving interruption of electrical connection in the battery pack; and wherein the first upper mounting members, the second upper mounting member, and the rear mounting member are formed in the shape of a quadrangular pipe in vertical section. (a) a battery module array comprising battery modules configured to have a structure in which battery cells or unit modules, each of which has two or more battery cells mounted therein, are stacked in an inverted state, the battery modules being arranged in two or more rows; (b) a pair of side support members (a front support member and a rear support member) configured to respectively support a front and a rear of the battery module array in a state in which the side support members are in tight contact with outermost battery modules of the battery module array; (c) lower end support members coupled to lower ends of the side support members to support a lower end of the battery module array; (d) two or more first upper mounting members coupled to upper ends of the side support members and to lower ends of the inverted battery modules, one end of each of the first upper mounting members being fastened to an external device; (e) a second upper mounting member configured to vertically intersect the first upper mounting members, the second upper mounting member being coupled to upper ends of the first upper mounting members, opposite ends of the second upper mounting member being fastened to the external device; and (f) a rear mounting member located at a rear of the battery module array, opposite ends of the rear mounting member being fastened to the external device, wherein