Abstract: In assessing the effect of indoor emission sources, such as furniture and building materials which emit hazardous chemical substances to indoor environment, with respect to chemical substances emitted from each emission source; calculating a emission amount (Qn) of each emission source per time using parameter of a emission rate (Fn) of chemical substances emitted from each emission source per area and per time and a surface area (Sn) of each emission source; with the result, calculating individually an indoor concentration of a specific chemical substance when assuming that only each emission source is individually placed indoors; and outputting the individual indoor concentration as the fundamental data.