Flow-induced cavity noise has been investigated for a wall jet over an axisymmetric cavity. Aspect ratio of the cavity width to its height was varied from 0.5 to 1.5. Also, there exists another geometric parameter, that is, a thickness of the wall jet. In the present study, the thickness can be easily changed by movement of the axisymmetric cavity in the axial direction. Experimental results indicate that in a thinner wall jet the 2nd mode of the self-sustained oscillation is dominant, and that the dominant mode is in transition as its thickness increasing.