An armature for a rotating electrical machine, the armature includes a cylindrical core having a plurality of longitudinally extending slots that are dispersedly arranged in a circumferential direction; and coils wound around the slots, wherein each of the slots is formed such that an inner circumferential opening thereof that is open radially inwardly is smaller in a circumferential width than a slot interior positioned on a radially outer side of the inner circumferential opening, and linear conductors forming the coils are each formed to be larger in the circumferential width than the inner circumferential opening.