An experimental study was performed in order to explore characteristics of the leading flame edge of a spreading flame over a combustible material. The movement of gasifying region of the combustible solid beneath the flame was simulated using a velocity controllable experimental apparatus on which a burning PMMA (polymethylmethacrylate) piece was installed. In the experiments, the characteristics of the leading flame edge were examined by changing the velocity of apparatus from 0 to 100 cm/s after a stable flame was established on the piece. It was found a stable leading flame edge was kept when the velocity of apparatus, i.e. the velocity of the leading flame edge, was below a limiting velocity in between 30 cm/s similar to 40 cm/s in the present experiments. For the velocities of the leading flame edge below the limiting velocity, the leading flame edge was indicated to be very similar to those of the diffusion flames at the stagnation region.