A frame assembly (10, 20) for fixing a cell assembly formed by stacking one or more battery cells, comprising: a frame disposed to surround the cell assembly and provided with an upper plate and side plates connected to both ends of the upper plate; bus bars disposed on and fixed to the side plates; and a flexible circuit board disposed along the upper plate and the side plates to sense voltages of the battery cells, the flexible circuit board includes: a central portion having a band shape; first connection circuit portions formed at both ends of the central portion and disposed to face each other; second connection circuit portions extending from the first connection circuit portions in parallel with the central portion; and third connection circuit portions extending from the first connection circuit portions and the second connection circuit portions and connected to the bus bar, wherein the flexible circuit board further includes an overlapped portion including one portion of each of the second connection circuit portions and another portion of each of the second connection circuit portions overlapped with the one portion of each of the second connection circuit portions in a cross-sectional direction being formed when each of the second connection circuit portions is folded toward one side of each of the first connection circuit portions. a frame disposed to surround the cell assembly and provided with an upper plate and side plates connected to both ends of the upper plate; bus bars disposed on and fixed to the side plates; and a flexible circuit board disposed along the upper plate and the side plates to sense voltages of the battery cells, the flexible circuit board includes: a central portion having a band shape; first connection circuit portions formed at both ends of the central portion and disposed to face each other; second connection circuit portions extending from the first connection circuit portions in parallel with the central portion; and third connection circuit portions extending from the first connection circuit portions and the second connection circuit portions and connected to the bus bar, wherein the flexible circuit board further includes an overlapped portion including one portion of each of the second connection circuit portions and another portion of each of the second connection circuit portions overlapped with the one portion of each of the second connection circuit portions in a cross-sectional direction being formed when each of the second connection circuit portions is folded toward one side of each of the first connection circuit portions. a central portion having a band shape; first connection circuit portions formed at both ends of the central portion and disposed to face each other; second connection circuit portions extending from the first connection circuit portions in parallel with the central portion; and third connection circuit portions extending from the first connection circuit portions and the second connection circuit portions and connected to the bus bar, wherein the flexible circuit board further includes an overlapped portion including one portion of each of the second connection circuit portions and another portion of each of the second connection circuit portions overlapped with the one portion of each of the second connection circuit portions in a cross-sectional direction being formed when each of the second connection circuit portions is folded toward one side of each of the first connection circuit portions.