This invention includes a first filter (27) connected between a susceptor (21) and ground and having a variable impedance, a sensor (28) for detecting an electrical signal based on the state of a plasma (P) generated in a process chamber (11), and a control means (36) for controlling the impedance of the first filter (27) on the basis of a detection result output from the sensor (28). Thus, a preferable plasma distribution to match the object of the plasma process can be realized.