Patent ID: 7164271

Claim:
An ion current detecting device for detecting an ignition condition in an internal combustion engine comprising: a spark plug for generating a spark in a combustion chamber of the internal combustion engine and having a gap between electrodes; an ignition coil for supplying high voltage to the spark plug; and an ion current detecting unit for detecting ion current based on combustion ions generated after an ignition which is performed in the combustion chamber of the internal combustion engine, and the ion current detecting unit being electrically connected to the spark plug and the ignition coil, and including an amplifier unit for amplifying ion current detected by the ion current detecting unit, wherein an amplification rate of the amplifier unit has a first amplification rate for a small ion current level and a second amplification rate for a high ion current level, the amplifier unit sets that the second amplification rate to a lower level than the first amplification rate so that the amplified ion current output from the amplifier unit increases with an increase in the ion current value.