Self-excited oscillation of an axisymmetric jet impinging upon a ring is investigated experimentally. The discreat vortices impinge upon the downstream sharp edge of the ring, in turn producing an upstream influence, thereby closing the loop for sustaining oscillations, as confirmed by the form of phase analysis of velocity and pressure signals. The fundamental frequency component exhibits an overall phase difference of (2nπ) +1/2 (n=0, 1, 2) between the nozzle lip and edge. Furthermore, the fundamental component propagates with phase speed, which is about 0.52〜0.59U_o. Spectral analysis of velocity fluctuation reveals multiple frequency components having substantial amplitudes relative to that of the fundamental frequency component ; using coherence analysis it is shown that the lowest frequency component can interact with the fundamental component either to reinforce itself or to produce an additional frequency component.