A single-phase reactor includes an outer peripheral iron core, at least four iron cores, which are in contact with or coupled to the inner surface of the outer peripheral iron core, and coils which are wound around at least two iron cores of the at least four iron cores. Gaps, which can be magnetically coupled, are each formed between two adjacent ones of the at least four iron cores, or are formed between the at least four iron cores and a central iron core positioned at the center of the outer peripheral iron core.