An electric power steering apparatus for supplying a steering assist torque from an electric motor to a steering mechanism including a torque limiter which comprises a case made of a magnetic material and secured to an output shaft of the electric motor, a boss made of a magnetic material concentrically rotatably arranged relative to the case and connected to a driven shaft, and a permanent magnet member disposed between the case and the boss for magnetically connecting therebetween. The permanent magnet member is annular and has an axially anisotropic magnetization of a negative temperature coefficient of residual magnetic flux density. The apparatus comprises a layer of an abrasion-resistant material provided between the permanent magnet member and at least one of the case and the boss and a cover for covering the outside of the case and the boss. At least one of the case and the boss comprises a guide portion for guiding and supporting at least one of an outer circumference surface and an inner circumference surface of the permanent magnet member that is annular as well as a seal portion for sealing at least one of the outer circumferential surface and the inner circumferential surface of the other of the case and the boss against the entry of any foreign matter.