A linear and a fully nonlinear numerical wave tanks (NWTs) were applied to study wave drift force acts on a two-dimensional Lewis form body in finite depth wave flume. These NWTs are based on potential theory and the fluid and floating body motions are directly simulated in time domain. Boundary value problems both on the velocity potential φ and its time derivative ∂φ/∂ t are solved at each time step. The coupling condition between fluid and floating body is imposed as the implicit boundary condition of ∂φ/∂ t on wetted body surface. The radiation condition at both tank ends are satisfied by artificial damping technique. Using these NWTs, effects of the floor step of the flume on wave drift force were studied. Measurement of wave drift force was also conducted in our two dimensional wave flume. In this report, the results of simulations and measurements are presented and the effect of the floor step on wave drift force is discussed.