Provided is a reactor which uses a reactor core in which J-shaped iron cores are oppositely disposed in a ring shape. In the ring shape, an axial outer circumferential part of a first coil wound around a first gap and an axial outer circumferential part of a second coil wound around a second gap overlap each other in an axial direction. Regarding four holding stay parts disposed at four corners of the reactor, the rigidity of the holding stay parts close to the first gap and the second gap is lower than the rigidity of the holding stay parts far from the first gap and the second gap.