A control device of an internal combustion engine having a variable valve train (11, 14) capable of variably-controlling opening/closing time or a lift amount of at least one of an intake valve and an exhaust valve, and a turbo charger, the control device comprising: internal EGR scavenging ratio arithmetic operation means for, when intake pressure becomes higher in comparison with exhaust pressure in a charging status, performing an arithmetic operation to obtain an internal EGR scavenging ratio representing a value which is calculated such that it represents an internal EGR ratio in accordance with actual engine operation, wherein the internal EGR ratio in accordance with actual engine operation decreases by scavenging from a cylinder to an exhaust pipe as an overlap duration in which both the intake valve and the exhaust valve are opened increases; and means for controlling the overlap duration so as to control said obtained internal EGR scavenging ratio to a predetermined ratio, characterized in that said control device further comprises: an air-fuel ratio sensor for detecting an air-fuel ratio of unburned gas supplied into the cylinder based on a non-gas component flowing through the exhaust pipe; and means for determining presence/absence of blow-by of unburned gas from the intake pipe via the cylinder to the exhaust pipe in the overlap duration based on an output value from said air-fuel ratio sensor; and when said means for determining presence/absence of blow-by of unburned gas determines that there is blow-by of unburned gas, said control device feed-back controls the variable valve train (11, 14) to reduce the overlap duration. internal EGR scavenging ratio arithmetic operation means for, when intake pressure becomes higher in comparison with exhaust pressure in a charging status, performing an arithmetic operation to obtain an internal EGR scavenging ratio representing a value which is calculated such that it represents an internal EGR ratio in accordance with actual engine operation, wherein the internal EGR ratio in accordance with actual engine operation decreases by scavenging from a cylinder to an exhaust pipe as an overlap duration in which both the intake valve and the exhaust valve are opened increases; and means for controlling the overlap duration so as to control said obtained internal EGR scavenging ratio to a predetermined ratio, characterized in that said control device further comprises: an air-fuel ratio sensor for detecting an air-fuel ratio of unburned gas supplied into the cylinder based on a non-gas component flowing through the exhaust pipe; and means for determining presence/absence of blow-by of unburned gas from the intake pipe via the cylinder to the exhaust pipe in the overlap duration based on an output value from said air-fuel ratio sensor; and when said means for determining presence/absence of blow-by of unburned gas determines that there is blow-by of unburned gas, said control device feed-back controls the variable valve train (11, 14) to reduce the overlap duration. an air-fuel ratio sensor for detecting an air-fuel ratio of unburned gas supplied into the cylinder based on a non-gas component flowing through the exhaust pipe; and means for determining presence/absence of blow-by of unburned gas from the intake pipe via the cylinder to the exhaust pipe in the overlap duration based on an output value from said air-fuel ratio sensor; and when said means for determining presence/absence of blow-by of unburned gas determines that there is blow-by of unburned gas, said control device feed-back controls the variable valve train (11, 14) to reduce the overlap duration.