In detecting the unignited state of plasma based on a reflected wave, false detection during a normal plasma ignition time is prevented so as to detect the unignited state during plasma abnormality. When a pulse output is supplied to a plasma load by pulse driving from an RF power source, the unignited state of plasma abnormality is detected on the basis of the continuous state of the reflected wave, whereby a total reflected wave generated in the unignited state during plasma abnormality is detected in distinction from the reflected wave generated in the normal ignited state. With this configuration, in detecting the unignited state by comparing a peak value of the reflected wave with a threshold, it is possible to prevent that a reflected wave generated in the normal ignited state is erroneously detected as the total reflected wave that is generated in the abnormal unignited state.