Disclosed is an ion source comprising a plate-shaped source body which has radioactivity on its both sides and allows positive and negative ions to penetrate through the source body. The present invention gives beneficial effects. First, the ion source structure can improve the ionization efficiency of sample molecules, and the generated sample ions have a centralized distribution within a flat space on both sides of the source body. Such distribution of ion cloud facilitates to improve the IMS sensitivity. Meanwhile, the source body of the present invention has a transmittance in itself. Thus, positive and negative ions generated on both sides of the source body can penetrate through the source body and be separated to the both sides of the source body. In this way, it is possible to improve the utilization efficiency of ions.