© 2018, The Japan Wood Research Society. We developed a new system for measuring the NO2 sorption ability of Japanese cedar (Cryptomeria japonica) wood by referring to Japanese Industrial Standard for JIS R 1701-1 (Test method for air purification performance of photocatalytic materials, Japanese Standard Association, Tokyo, 2004). Aeration experiments were conducted using plated specimen, particle specimen, discoid specimen and wood powder with consideration of aeration condition and surface area which can contact with NO2 gas. In the plated specimen, the NO2 sorption ability was greatly affected by the thickness of longitudinal direction, and high NO2 sorption ability of the transverse section was observed within a thickness range from the surface to ca. 3 mm. The average NO2 sorption volume for discoid specimen for 5 h was approx. five times larger than that those for the plated and particle specimens, which the thickness of longitudinal direction was 1.5 mm. This means that the NO2 sorption effect was especially high under the condition where the NO2 gas passed through tracheid. Also, it was suggested that the interface area between NO2 gas and specimen influenced to the NO2 sorption ability. Furthermore, it was confirmed that the NO2 sorption volume in discoid specimen and the grain size below 0.25–0.50 mm of wood powder reached the greatest.