The ring-velocimeter coupled with a hot wire/film probe was developed and has been applied to wind and water tunnel experiments in Fluids Engineering Laboratory of Nagaoka University of Technology. In this study, the hot-wire/film probe is replaced by a cantilever attached by a strain gauge to detect the drag acting on the ring. The vortex shedding frequency from the ring is determined from the drag fluctuation by applying the spectrum analysis, and the flow velocity in turn since it is proportional with the vortex shedding frequency. This technique for flow velocity measurement is robust in the sense that it is strong against the noise or decay of the detected signal since the dominant frequency is insensitive to such disturbances, and that the detecting probe is strong against the contaminants or particles/objects carried by the fluid. These advantages, together with its simple and cheap characteristics, make it possible to apply to natural water flow with severe conditions.