This work was undertaken for the numerical analysis of defrosting phenomena of automobile windshield. To analyze the defrost, the flow and temperature field of cabin interior, heat transfer through the windshield glass, and phase change of the frost should be analyzed simultaneously. The flow field was obtained by solving the 3-D unsteady Navier-Stokes equation and the temperature field was computed by energy equation. The phase-change process of Stefan problem was solved by enthalpy method. For code validation, the temperature field of the driven cavity was calculated. The result of calculation shows a good agreement with the other numerical results. Then, the present code was applied to the defrosting analysis of a real automobile and, also, a good agreement with experiment was obtained.