In this study, the microscopic visualization of the pyrolysis of woody biomass was conducted using the BL20B2 beamline at “SPring-8,” a large synchrotron radiation facility. Changes in the shape and internal structure of the woody biomass were visualized using ultra-high-speed computerized tomography (CT). The sample was a Japanese cypress wood with a height of 5 mm and diameter of 5 mm. We used radiation as the heat source to achieve a high heat flux. When the heat flux is high, the sample expands. Gaps were observed in the sample. Compared with the experimental results under the low heat flux obtained in the previous study ¹⁾, we observed a completely different aspect. In a nitrogen or air atmosphere, the internal structure of the wood during transient pyrolysis was visualized using ultra-high-speed X ray CT. In addition, the schlieren method was used to study the pyrolysis behavior of the woody biomass and the behavior of the pyrolysis gases.