An internal-combustion-engine combustion state detecting apparatus is configured in such a way as to include a circulation unit that short-circuits a primary winding so as to form a circulation path including the primary winding, while a spark discharge is produced in an ignition plug, and a circulation current control unit that controls a circulation current flowing in the circulation path and in such a way that based on an ion current detected by an ion current detection apparatus, the combustion state of an inflammable fuel-air mixture is detected.