In this study, the effectiveness of an oscillating-body WEC with a tuned inerter (TI) proposed by the authors is shown through wave flume testing. The TI mechanism consisting of a tuning spring, a rotational inertial mass, and a viscous damping component is able to increase energy absorption capability by taking advantage of the resonance effect of the rotational mass. This mechanism has been recently introduced for civil structures subjected to external loadings such as earthquakes and winds to decay vibration response immediately. The authors applied this mechanism to oscillating-body WECs and showed that the proposed WEC increased the power generation performance and broadened the effective frequency range without increasing the mass of the buoy itself through numerical simulation studies. To verify the validity of the proposed WEC experimentally, a small-scale prototype of the proposed device is designed and wave flume testing is carried out with various regular wave inputs of different frequencies. The results show that the WEC with the properly adjusted TI mechanism demonstrates better power generation performance compared to the conventional WEC over a wide range of wave frequencies.