The confinement physics of the improved H-mode is analysed in detail. It is shown that this scenario can be largely unified with that of the standard H-mode. Transport barriers exist in the early phase of the discharge just after the switch on of the heating. In steady state, however, no clear internal transport barriers can be indentified in the ion temperature profiles. The profiles are then found to be stiff and the improved H-mode follows the same ion temperature scaling as the standard H-mode. The improvement of the confinement against the H-mode scaling is partly due to the dependence of this scaling on the line averaged density, and is partly obtained through density peaking appearing at low densities. It is shown that pre-heating is not essential in reaching the good confinement.