The pyrolysis gas pressure and temperature inside of ablator pieces are measured in the arc-heated wind tunnel. Obtained pressure and temperature data are compared with those given by the SCMA code that accounts for unsteady ablation. In the SCMA code, the motion of pyrolysis gas is calculated by solving the mass and the momentum conservation equations with assuming a finite permeability determined in this study. Though a quantitative agreement is not yet accomplished, the measured pressure profile that increases initially, turns to decrease and then reaches to a plateau is reproduced qualitatively by the SCMA code. It is suggested from the experimental data and the computed result that delamination of ablator likely occurs at the region where ablator is not fully charred but partially pyrolyzed resulting in a smaller porosity and higher pyrolysis gas pressure.