Abstract: In a circulator comprising at least three ports, a pair of opposing conductors providing the ports, and a ferrimagnetic piece between the conductors, a gap appearing between the ferrimagnetic piece and the conductor or conductors is taken up by a spring member located in the gap. The conductors serve as an opposing pair of conductors of a waveguide of the circulator. Alternatively, the conductors serve as ground plates of a stripline with a center conductor disposed between the ground plates and with a pair of ferrimagnetic pieces disposed on both sides of the center conductor between the ground plates. In the latter case, a pair of spring members is preferably located between the ferrimagnetic pieces and the respective ground plates. Preferably, the spring member is made of phosphor bronze and comprises a plate in contact with the ferrimagnetic piece and legs extended from the plate towards the respective ports and brought into contact with the adjacent one of the opposing conductors.