A lithographic apparatus including an illumination system configured to condition a radiation beam is described. The illumination system includes radiation beam uniformity adjuster for adjusting the uniformity of the radiation beam using segments that are at least partly arranged in the radiation beam and that are mounted on a frame by a torsion bar. The device further includes an actuator configured to rotate the segment in order to change the amount of radiation of the radiation beam that is blocked. The device also includes a first magnetic member mounted on the torsion bar configured to co-operate with a second magnetic member mounted on the frame for generating a position dependent torque about the longitudinal axis that is configured to at least partly compensate a torque exerted on the segment by the torsion bar.