Flexible printed circuit board

A flexible printed circuit board (20) is robust to a repeated twisting and consists of a minute circuit printed on a flexible insulated material sheet, and has the bent parts (21,21') of the opposite edges symmetrical in structure. The bent parts (21,21') are straightened out when twisting occurs. In the flexible printed circuit board (20), the opposite edges are longer in length than the middle part such that the tensile deformation at the opposite edges at the time of twisting does not occur or is minimized.