A simple diffuse-boundary model is considered for magnetohydrodynamic equilibrium in an axisymmetric torus with rectangular cross-section. The pressure balance equations are reduced from the expressions for eigenvalues of the equilibrium equation. The parameter βp (ratio of plasma pressure to poloidal magnetic pressure) is closely related to the paramagnetism of the plasma and to geometrical factors. The condition of no reversed toroidal current gives the limitation on paramagnetism and βp+. The critical βp becomes largest for square plasma cross-section.