A battery pack for an electric vehicle, mounted on an electric vehicle, comprising: a tray which accommodates a battery and which is formed in a box-like shape having an opening on an upper side; and at least one outer frame disposed on an outer side of a side wall surface of the tray, the outer frame extending along the side wall surface and being welded to the side wall surface so as to cover the side wall surface, wherein the at least one outer frame is constituted of a plate member or a combination of plate members, the at least one outer frame including: a first protruding section welded to an outer bottom surface of the tray; a second protruding section positioned above the first protruding section and formed to protrude outwardly from the tray; an outer section connecting the first protruding section and the second protruding section at a position outwardly spaced from the side wall surface of the tray; and an inner section extending from the second protruding section toward the first protruding section and being welded to the side wall surface of the tray, wherein the first protruding section, the second protruding section, the outer section and the inner section form a part of a closed cross section of the at least one outer frame, wherein the outer section includes an aperture facing the inner section, and wherein the aperture is to weld the inner section and the side wall surface of the tray with each other, and is formed to have a size which allows a welding gun for spot welding to be inserted through the aperture. a tray which accommodates a battery and which is formed in a box-like shape having an opening on an upper side; and at least one outer frame disposed on an outer side of a side wall surface of the tray, the outer frame extending along the side wall surface and being welded to the side wall surface so as to cover the side wall surface, wherein the at least one outer frame is constituted of a plate member or a combination of plate members, the at least one outer frame including: a first protruding section welded to an outer bottom surface of the tray; a second protruding section positioned above the first protruding section and formed to protrude outwardly from the tray; an outer section connecting the first protruding section and the second protruding section at a position outwardly spaced from the side wall surface of the tray; and an inner section extending from the second protruding section toward the first protruding section and being welded to the side wall surface of the tray, a first protruding section welded to an outer bottom surface of the tray; a second protruding section positioned above the first protruding section and formed to protrude outwardly from the tray; an outer section connecting the first protruding section and the second protruding section at a position outwardly spaced from the side wall surface of the tray; and an inner section extending from the second protruding section toward the first protruding section and being welded to the side wall surface of the tray, wherein the first protruding section, the second protruding section, the outer section and the inner section form a part of a closed cross section of the at least one outer frame, wherein the outer section includes an aperture facing the inner section, and wherein the aperture is to weld the inner section and the side wall surface of the tray with each other, and is formed to have a size which allows a welding gun for spot welding to be inserted through the aperture.