In order to pivot a pivotal arm (60) carrying an optical scanner (5), use is made of at least one coil (13) and at least one permanent magnet (16, 17), the coil being arranged on the pivotal arm or on a frame supporting the arm and the permanent magnet being arranged on the frame or on the arm. The coil (13) has a substantially straight active coil section (14) which is arranged near the pivotal axis (8) about which the pivotal arm is pivotable and which extends transversely of the longitudinal axis of the pivotal arm. The ends of this coil section are interconnected by a further coil section (15) which is, for example, concentric with the pivotal spindle and which extends at that side of the pivotal axis which is remote from the scanning unit.