We investigate the anomalous heat conduction in a tokamak plasma analytically and computationally. Our toroidal particle simulation shows a new emerging physical picture that the toroidal plasma exhibits marked properties distinct from a cylindrical plasma: (i) the development of radially extended potential streamers localized to the outside of the torus, (ii) more robust ion temperature gradient instability, (iii) radially constant eigenfrequency, (iv) global temperature relaxation, and (v) radially increasing heat conductivity &khgr;i. These results are analyzed by linear and quasilinear kinetic theory. A relaxation theory based on the reductive perturbation theory in the quasilinear equation is developed. The theory constrains the thermal flux so that &khgr;iincreases radially. The Bohm‐like scaling is found in connection with the radially extended mode structure.