PURPOSE: A radial disc type ion mobility analyzer is provided to improve precision by including a dummy electrode for noise compensation and to accurately and rapidly detect a chemical substance existing in the air under the atmospheric pressure state. CONSTITUTION: A partition member(40) has a hollowed cylindrical shape. A central line of shutter grid electrodes(15, 16) is matched with a central line of the partition member. A first electrode is placed in the inner side of the shutter grid electrodes. A second electrode is installed in the inner side of the first electrode. The second electrode comprises a route in order to receive sample gas from outside. An entrance of the route is connected to outside the partition member and an exit of the route is connected to inside the partition member. A detector electrode(31) is fixed to the radial direction inner circumference of the partition member.
