Abstract: Judgment, such as whether if the present rotation is normal, or whether if there is a risk of synchronicity loss, could be performed, and further, a most suitable control could be performed by detecting a change in drive current of a stepping motor, judging a load, and generating a signal.

Abstract: A balancing device (11) has a first balance pulley (20) provided in a hoisting drum (3) and a second balance pulley (40) connected to a coil spring (31). These pulleys are connected through a tension wire (50). The first balance pulley has a main pulley portion (25) for taking-up the tension wire at the beginning of a feed-out process from a fully opened position, and a zero-point return pulley portion (26) for taking-up the tension wire from halfway. The zero-point return pulley portion has an outer circumferential shape in which the tension wire passes the pulley axial center at a fully shut position. The second balance pulley (40) has a cylindrical portion (46) for feeding-out the tension wire at the beginning of the feed-out process from the fully opened position, and a conical portion (47) for feeding-out the tension wire from halfway. The conical portion has a shape in which its diameter is smaller on the cylindrical portion side.