A frame assembly for fixing a plurality of stacked battery cells, the frame assembly comprising: a frame including an upper surface, a first side surface connected to a first end of the upper surface and a second side surface connected to a second end of the upper surface, the frame being configured to enclose the plurality of stacked battery cells; a plurality of first bus bars (121, 122) disposed on the first side surface; a plurality of second bus bars (131, 132) disposed on the second side surface; and a flexible printed circuit board disposed along the upper surface, the first side surface, and the second side surface of the frame, the flexible printed circuit board being configured to sense the plurality of stacked battery cells, wherein the flexible printed circuit board comprises: a circuit portion disposed on the upper surface; a first connection circuit portion extending from a first end of the circuit portion and coupled to the plurality of first bus bars (121, 122); and a second connection circuit portion extending from a second end of the circuit portion and coupled to the plurality of second bus bars (131, 132), wherein each of the first and second connection circuit portions (210, 220) comprises: a conductive substrate layer (2112, 2122, 420) made of a flexible material; a first insulating layer (2111, 2121, 410) disposed on a first surface (2112a, 2122a, 421) of the substrate layer and having at least one first opening (2111a, 2122a, 410a) formed therein so as to expose the first surface of the substrate layer; and a second insulating layer (2113, 2123, 430) disposed on a second surface (2112b, 2122b, 422) of the substrate layer and having at least one second opening (2113a, 2123b, 430a) formed at a position opposite the at least one first opening with respect to the substrate layer so as to expose the second surface of the substrate layer, wherein the second surface of the substrate layer of the first connection circuit portion is bonded to the plurality of first bus bars (121, 122), and wherein the second surface of the substrate layer of the second connection circuit portion is bonded to the plurality of second bus bars (131, 132). a frame including an upper surface, a first side surface connected to a first end of the upper surface and a second side surface connected to a second end of the upper surface, the frame being configured to enclose the plurality of stacked battery cells; a plurality of first bus bars (121, 122) disposed on the first side surface; a plurality of second bus bars (131, 132) disposed on the second side surface; and a flexible printed circuit board disposed along the upper surface, the first side surface, and the second side surface of the frame, the flexible printed circuit board being configured to sense the plurality of stacked battery cells, wherein the flexible printed circuit board comprises: a circuit portion disposed on the upper surface; a first connection circuit portion extending from a first end of the circuit portion and coupled to the plurality of first bus bars (121, 122); and a second connection circuit portion extending from a second end of the circuit portion and coupled to the plurality of second bus bars (131, 132), a circuit portion disposed on the upper surface; a first connection circuit portion extending from a first end of the circuit portion and coupled to the plurality of first bus bars (121, 122); and a second connection circuit portion extending from a second end of the circuit portion and coupled to the plurality of second bus bars (131, 132), wherein each of the first and second connection circuit portions (210, 220) comprises: a conductive substrate layer (2112, 2122, 420) made of a flexible material; a first insulating layer (2111, 2121, 410) disposed on a first surface (2112a, 2122a, 421) of the substrate layer and having at least one first opening (2111a, 2122a, 410a) formed therein so as to expose the first surface of the substrate layer; and a second insulating layer (2113, 2123, 430) disposed on a second surface (2112b, 2122b, 422) of the substrate layer and having at least one second opening (2113a, 2123b, 430a) formed at a position opposite the at least one first opening with respect to the substrate layer so as to expose the second surface of the substrate layer, wherein the second surface of the substrate layer of the first connection circuit portion is bonded to the plurality of first bus bars (121, 122), and wherein the second surface of the substrate layer of the second connection circuit portion is bonded to the plurality of second bus bars (131, 132). a conductive substrate layer (2112, 2122, 420) made of a flexible material; a first insulating layer (2111, 2121, 410) disposed on a first surface (2112a, 2122a, 421) of the substrate layer and having at least one first opening (2111a, 2122a, 410a) formed therein so as to expose the first surface of the substrate layer; and a second insulating layer (2113, 2123, 430) disposed on a second surface (2112b, 2122b, 422) of the substrate layer and having at least one second opening (2113a, 2123b, 430a) formed at a position opposite the at least one first opening with respect to the substrate layer so as to expose the second surface of the substrate layer, wherein the second surface of the substrate layer of the first connection circuit portion is bonded to the plurality of first bus bars (121, 122), and wherein the second surface of the substrate layer of the second connection circuit portion is bonded to the plurality of second bus bars (131, 132).