A torsion washer integrally formed as a one-piece structure includes an external ring-shaped portion, a first abutting arm and a second abutting arm both separately extending from an inner edge of the external ring-shaped portion, and a connecting lever connecting the first and second abutting arms. The inner edge includes a first arc segment and an opposite second arc segment, and centers of circle of the first and second arc segments are located in a space surrounded by the inner edge. Free ends of the first and second abutting arms do not contact the inner edge. A distance between a first abutting portion of the first abutting arm and the first center of circle is less than a radius of the first arc segment. The connecting lever is spaced apart from the inner edge, allowing the first and second abutting arms to be interlinked with each other.