A window lifter comprises a cable, a window linkage driven by the cable, a fixed device and a cable redirecting device. The cable redirecting device is rotatably mounted on the fixed device and adapted to automatically lock onto the fixed device upon reaching a predetermined angular position. In addition, the cable redirecting device has a cable guiding portion which is not a figure of revolution about the axis of rotation relative to the fixed device. This window lifting mechanism provides a simple structure with few elements. Its assembly is also simple: the cable-redirecting device is rotatably mounted on the fixed device; it is thereafter rotated for tensioning the cable and then locked in a position where the cable is tensioned.