PURPOSE: To achieve safety and low noise generation without causing damage of bearings and gears with abrasive dust such as iron powder as foreign matter by allowing a permanent magnet furnished at the bottom of a gear box to attract the iron powder contained in a lubricating oil.

CONSTITUTION: A permanent magnet 31 and an iron wire layer 33 are furnished at the bottom 11b of a gear box 11. Accordingly the abrasive dust of gears, etc., floating in a lubricating oil 34 is attracted by the magnet 31 or to the layer 33 magnetiozed thereby. The attracted abrasive dust will not be separated even though the lubricating oil 34 is stirred by rotation of gears. Besides the effect to attract the abrasive dust, the iron wire layer 33 exerts a good effect of preventing separation of abrasive dust likely with stirring. This eliminates occurrence of poor operation due to abrasive dust, prevents failure in roller bearings, precludes damage of gear flanks, and enhances the stability and reliability of the performance as a winch device of elevator.