Large scale, DC type plasma convection is investigated in the JFT-2M tokamak. In the plasma edge region, E*B type convective flows are observed, which are caused by interactions with both a poloidal limiter and an RF wave injection. Observation of changes in the edge potential during lower hybrid (LH) wave injection indicated that the confinement improvement in the LH phase is due to the reduction of an intrinsic E*B type convection. These results are used in the construction of a model that explains both the L and H modes found in the tokamak NBI experiments. The model consists of both a deterioration mechanism based on the obstacle induced convection and a recovery due to the increase of the electric conductivity along the magnetic field. Agreement between the model and typical experimental results is shown