A stator of a rotating electrical machine includes a stator core, plural stator coil groups constituting plural phases, plural pieces of interphase insulation paper for insulation of coils belonging to different phases, and plural connecting strips formed integrally with the interphase insulation paper pieces. Each interphase insulation paper piece has ends inserted between coil ends of unit coils belonging to an identical phase thereby to function as interphase insulation paper for insulation of coils belonging to the identical phase. Each interphase insulation paper piece for insulation of coils belonging to the different phases, functioning as the interphase insulation paper piece for insulation of coils of the identical phase, insulates between coil ends of the first unit coils of respective first and second series circuits constituting the inner circumference side phase and a coil end of the unit coil constituting the outer circumference side phase.