To simplify sealing of a lubricating chamber in an electric power steering device in which teeth of a worm wheel that transmits the rotation of an electric motor are arranged in the lubricating chamber.

In the electric power steering device, the teeth 64 of the worm wheel 60 are arranged in the lubricating chamber 70 divided by a housing 20 and sealing means 80, 90, which seal a lubricant of the lubricating chamber 70 within the lubricating chamber 70, are provided each at both sides of the teeth 64 of the worm wheel 60. The sealing means 80 provided at least at one side of the teeth 64 of the worm wheel 60 is structured with a seal ring 81 that is fixed to either of the wall surface of the housing 20 and the side surface of the worm wheel 60 and contacts the other surface slidably.