In order to investigate regional absorption of carbon dioxide (CO2) by forests in Japan, first, focusing on an experimentally obtained relation between photosynthetic rate of a tree and atmospheric CO2 concentration around the tree, the atmospheric CO2 concentration dependence of CO2 absorption rate of forests has been described by a Michaelis-Menten type function. Secondly, from the viewpoint of local region for operating area of electric power companies, CO2 absorption by forests has been investigated for different three cases with a simple model in which the atmospheric CO2 concentration around artificial forests are artificially increased up to 1,000 ppm. The resultant CO2 absorption by forests much depends on the atmospheric CO2 concentration, and will be effectively promoted by an easy artificial treatment. Those results might be useful to design a biomass energy carbon capture storage system toward a sustainable society. © Springer 2011.