An electric motor includes a stator, a rotor having a rotating shaft, first and second bearings each having an outer ring, balls, and an inner ring, and spaced apart axially from each other, a preload washer including a shaft section having a preset fixed length in the axial direction, and an elastically-deformable portion extending from one end portion of the shaft section to be elastically deformable, the preload washer applying a preset intensity of preload to the inner ring of the first or second bearing, and a coupling member screwed into an end portion of the rotating shaft and elastically deforming the preload washer in the axial direction. This structure may result in preventing an excessive preload from being applied to the bearing and allowing a preset preload to be stably maintained when thrust is applied.