To provide an electric power steering device that realizes effective suppression of noises caused by backlash between a worm and a worm wheel.

In a worm shaft 55, first and second flanges 71, 73 are formed confronting first and second bearing 59, 61, respectively and a magnetic repulsion mechanism 81 is set between the first and second flanges 71, 73 and the first and second bearings 59, 61. The magnetic repulsion mechanism 81 comprises first and second annular permanent magnets 83, 85 fitted at the outside of the worm shaft 55 and the first permanent magnet 83 contacts both of the flanges 71, 73 of the worm shaft 55 and the second permanent magnet 85 contacts collars 63, 65. Both of the permanent magnets 83 and 85 are the same members polarized axially, and arranged so that the same poles thereof are confronted with each other.