The purpose of this study is to investigate unsteady characteristics of the annular impinging jet. Water and air were employed as working fluids. Two pressure transducers made of a semiconductor were installed, one being at the center of the disk placed downstream end of a inner tube and the other on an impinged flat plate. Cross-spectrum and cross-correlation functions of pressures were measured by varying a distance H between the annular nozzle and the impinged flat plate. It was found that there were four types of distinguishable frequencies for pressure, according to a value of H. It was ascertained that fluctuations with the large scale of the annular impinging jet had essentially two modes and the frequencies of these changed linearly with an issuing velocity alone of the annular jet. Some discussion of a cause of their generation took place.