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