A battery pack comprising: (a) a battery module array having battery modules arranged in two or more rows, each of the battery modules being 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 a state in which the battery cells or the unit modules are erected in an upside-down fashion; (b) a pair of side supporting members comprising a front supporting member and a rear supporting member to support a front and rear of the battery module array, respectively, in tight contact with outermost battery modules of the battery module array; (c) lower end supporting members coupled to lower ends of the side supporting 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 supporting members and lower ends of the battery modules, one end of each of the first upper mounting members being fastenable to an external device; (e) a second upper mounting member coupled to upper ends of first upper mounting members such that the second upper mounting member intersects the first upper mounting members at right angles, opposite ends of the second upper mounting member being fastenable to the external device; (f) a rear mounting member disposed at a rear of the battery module array, opposite ends of the rear mounting member being fastenable to the external device; and (g) a bracket coupled between at least one of the side supporting members and the rear mounting member to distribute load of the battery modules to the rear mounting member via the side supporting members. (a) a battery module array having battery modules arranged in two or more rows, each of the battery modules being 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 a state in which the battery cells or the unit modules are erected in an upside-down fashion; (b) a pair of side supporting members comprising a front supporting member and a rear supporting member to support a front and rear of the battery module array, respectively, in tight contact with outermost battery modules of the battery module array; (c) lower end supporting members coupled to lower ends of the side supporting 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 supporting members and lower ends of the battery modules, one end of each of the first upper mounting members being fastenable to an external device; (e) a second upper mounting member coupled to upper ends of first upper mounting members such that the second upper mounting member intersects the first upper mounting members at right angles, opposite ends of the second upper mounting member being fastenable to the external device; (f) a rear mounting member disposed at a rear of the battery module array, opposite ends of the rear mounting member being fastenable to the external device; and (g) a bracket coupled between at least one of the side supporting members and the rear mounting member to distribute load of the battery modules to the rear mounting member via the side supporting members.