An armature assembly apparatus for assembling an armature of an electrical machine is provided. The armature assembly apparatus has an armature holding apparatus to hold a partially assembled armature such that a rotation axis of the armature is horizontal. The armature assembly apparatus has a rotating device for rotating the partially assembled armature about a rotation axis. The armature assembly apparatus also has a ring segment conveyance for conveying an armature ring segment to a mounting position relative to a free ring segment portion of the partially assembled armature.