Disclosed is a combustion state detection apparatus for an internal combustion engine, which is capable of detecting abnormal combustion with high accuracy. The combustion state detection apparatus for an internal combustion engine includes: a variety of sensors; an ignition coil; an ignition plug; a transistor; a switching control unit; an ion current detection unit; and abnormal combustion detection units for determining that abnormal combustion has occurred in a case where a crank angle at a point of time when the ion current exceeds a predetermined current value or when the ion current that exceeds the predetermined current value reaches a peak value thereof is on a spark-advance side compared with a crank angle for determining abnormal combustion. The switching control unit ends the spark discharge at a predetermined timing while the spark discharge is in progress after the primary current is shut off and the spark discharge is generated.