A high-frequency input voltage and a high-frequency input current to a series resonant circuit are detected by a voltage detection unit and a current detection unit, respectively, and plasma input power is detected by a plasma input power detection unit based on the detected high-frequency input voltage and high-frequency input current. By directly detecting the plasma input power in this manner, the plasma input power may be accurately controlled regardless of the state of a plasma-generating gas or an analysis sample. Also, use of a switching circuit including a semiconductor device allows an inexpensive configuration compared with a configuration where a vacuum tube or the like is used.