An internal-combustion-engine combustion condition detection apparatus is provided with an ignition means that makes an ignition plug ignite a fuel; an ignition control means that controls the operation of the ignition means; an ion-current detection means that detects an ion current generated; an ion current detection range setting means that sets an ion-current detection range; a preignition detection means that detects preignition within a detection range to be set; a leakage current detection range setting means that sets a leakage-current detection range; and a leakage current determination means that determines whether or not a smolder exists, based on a current detected, within a detection range to be set, by the ion-current detection means. The ignition control means includes a non-combustion-stroke ignition control means; the leakage-current detection range set by the leakage current detection range setting means is set within the non-combustion stroke.Accordingly, both a smolder detection and a preignition detection can securely be performed.