In this study, the experimental and numerical analyses have been performed to study the ignition of solid fuel (PMMA) in the rectangular enclosure, when it is suddenly exposed to a radiative source with high emissivity. Experimentally, a high-speed camera has been used to record the flame initiation and propagation in the enclosure for various radiative heat source temperatures, while the ignition delay time as well as the gas phase temperature was measured. Numerical analysis has also been performed in a two-dimensional geometry by taking account of the effects of gas radiation due to fuel vapor. In general the ignition delay time decreased, as the radiative source temperature increased, while the ignition location shifted from the upper corner region of hot wall to the upper corner region of fuel wall in the rectangular enclosure. Thereby, the ignition mechanism seemed to be changed from the mixing and transported controlled ignition to the thermally controlled ignition. While the numerical ignition delays were in good agreement with the experimental ones for the former, numerical result under-predicted experimental one for the latter since the thermal pyrolysis of PMMA became more important than the heat and mass transfer process in the whole ignition process. Usage of numerical simulation was found to be also quite successful in examining and discussing flame behavior after onset of ignition, when the radiative heat source temperature was varied.