Complex free-surface flows in the vicinity of an obstacle placed on the floor of a channel to generate a surface wave has been studied experimentally and numerically. The numerical method examined is the simplified MAC method of Hirt & Nichol with the volume of fraction (VOF) method of treating the free surface. This calculation method used with a third-order upwind differencing scheme gives results that agree very well with experiments for not too large waves with relatively small velocities. The experiments show that as the flow volume and the velocity increase, the disturbances appear on the free surface with significant air entrainment. The present calculation method, although does not reproduce the detailes of the experiment exactly, shows appearance similar disturbances.