Carbon dioxide in atmosphere causes concrete carbonation which is the phenomenon, that is, the pH of concrete goes down from 12-13 to 8.85-10. Even though the carbon dioxide concentration of indoor is higher than that of outdoor, the micro measurement has not carried out. The concentration test was conducted three times in two rooms in a residential area, reading room in library, and lecture room. With all the deviation for each unit, the measured average value was 463.1~1425.3(ppm) which is more than three times than that of outdoor at the most. Without surface finishings in FEM calculation, the depth of carbonation is up to 4(cm). At the same time, the FEM calculation considering surface finishings. Any carbonation did not appeared because of the assumption, that is, surface finishings did not deteriorate.