A first and a second pulleys are rotatably supported at a fixed separation along a guide rail. A link arm is at one end pivotably connected to the axle of the first pulley and supports at the other end a drum which is rotatable manually or by an electric motor. A drive wire is fixed to the drum, sequentially wound around the first and second pulleys and finally secured to the drum. A window bracket, adapted to be secured to a window pane, is also secured to the wire so that rotation of the drum causes the wire and therefore the window pane to move along the guide rail. The regulator may include an additional pulley rotatably supported at a point opposite the first pulley with respect to the second pulley in which case, the drive wire is wound from the drum, around the first pulley, around the second pulley, around the additional pulley, around the first pulley again, and back to the drum. A device may be disposed near one of the second and additional pulleys to impart appropriate tension to the drive wire.