An electric power steering apparatus comprises an electric motor for producing a steering assist force, and a speed reduction mechanism for decelerating the rotation of an output shaft in the electric motor. The speed reduction mechanism comprises an input pulley driven by the electric motor, an output pulley connected to a steering shaft, and a belt for connecting the input pulley and the output pulley to each other. The belt comprises a helical toothed belt. The input pulley and the output pulley respectively include helical toothed pulleys meshed with the helical toothed belt.