An electric rotating machine is equipped with a middle core, an outer core disposed outside the middle core which rotates relative to the middle core, and an inner core disposed inside the middle core which rotates relative to the middle core. The middle core comprises plural plates disposed in an axial direction. The plural plates are connected in the axial direction by a connecting member, and joined to a first fixing member. The inner and outer circumferential surfaces are finished in the state where the plates are joined only to the first fixing member, and the opposite side to the first fixing member is joined to a second fixing member after finishing.