In the edge transport barrier of H-mode plasmas, a large poloidal flow exists and the electrostatic potential and density can have steep gradients both in the radial and poloidal directions. The accessibility to a two-dimensionally steep structure is demonstrated by solving the model equation including the poloidal structure, combined with the equation giving the time evolution of the radial electric field. The analysis is carried out with the parameter set of the electrode biasing experiment and shows the existence of the convective particle flux arising from poloidal inhomogeneity. This study provides an essential explanation for improving the transport analyses in H-modes by taking account of the two-dimensional effect in toroidal plasmas.