We theoretically analyze surface magnetoplasmon modes in a compact circular cavity made of magneto-optical material under a static magnetic field. Such a cavity provides two different methods for the surface wave to circulate in a unidirectional manner around the cavity, which offers more freedom, both in the one-way direction and in the frequency range, for designing nonreciprocal photonic components. We also show the interaction between this one-way cavity and waveguides through the example of a circulator, which lays the fundamental groundwork for potential nonreciprocal devices.