The purpose of this study is grasping characteristics of temporal and spatial changes of CO 2 gas concentration on the forest soil of three different types which is examination ground. (Young forest, Cedar forest and Oak forest) Results of this study are shown as follow. (1) CO 2 in every type of forest soil always is larger than 360ppm of that in the atmosphere．And, it also increased with increases of the soil-temperature with seasonal changes. (2)Regularity of CO 2 did not appear clearly in case of continuous observation for 24 hours, and CO 2 in forest soil was not greatly influenced by soil-temperature changes in a short time. (3)The positive correlation coefficient of the variations of two factors was recognized relationships between CO 2 in forest soil and soil temperature. Therefore, an estimated formula was obtained as a result of analysis by the measurement result of three different types examination ground.