Knocking frequency components passing through {HEAD ~ a band pass filter} 32 and frequency components lower than the knocking frequency and passing through {TAIL ~ a low load noise band pass filter} 321 are picked from the ionic current detected by an ionic current detecting unit 17 
Knocking frequency components passing through { HEAD ~ a band pass filter } 32 and frequency components lower than the knocking frequency and passing through { TAIL ~ a low load noise band pass filter } 321 are picked from the ionic current detected by an ionic current detecting unit 17
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH