A pyrolysis gasifier includes a tubular body configured to receive and pyrolyze a combustible waste, a bottom door disposed below the tubular body to selectively seal the tubular body, a main frame supporting the tubular body, a base frame supporting the bottom door, an automatic ash processor configured to, while traveling in one direction, push and remove ash remaining on the bottom door after pyrolysis of the combustible waste, and a guide frame supporting the automatic ash processor and configured to guide the travel of the automatic ash processor.