A control apparatus for an internal combustion engine, comprising: a supercharger that has a compressor that compresses air in an intake path; intake pipe pressure obtaining means that detects or estimates an intake pipe pressure; an intake variable valve apparatus capable of changing a valve timing of an intake valve; an exhaust variable valve apparatus capable of changing a length of a valve overlap period in which both said intake valve and an exhaust valve are open without changing the valve timing of said intake valve; the control apparatus being characterized by further comprising: storing means that stores information about a reference intake pipe pressure that is an intake pipe pressure on a boundary between a region where the amount of fresh air flowing in through said intake valve decreases when the valve timing of said intake valve is fixed and the length of the valve overlap period increases and a region where the amount of fresh air flowing in through said intake valve increases when the valve timing of said intake valve is fixed and the length of the valve overlap period increases; reference intake pipe pressure obtaining means that obtains the reference intake pipe pressure for the valve timing of said intake valve based on the information stored in said storing means; and blow-by determining means that determines the presence or absence of blow-by of fresh air into an exhaust side based on a result of comparison between the intake pipe pressure detected or estimated by said intake pipe pressure obtaining means and the reference intake pipe pressure obtained by said reference intake pipe pressure obtaining means. a supercharger that has a compressor that compresses air in an intake path; intake pipe pressure obtaining means that detects or estimates an intake pipe pressure; an intake variable valve apparatus capable of changing a valve timing of an intake valve; an exhaust variable valve apparatus capable of changing a length of a valve overlap period in which both said intake valve and an exhaust valve are open without changing the valve timing of said intake valve; the control apparatus being characterized by further comprising: storing means that stores information about a reference intake pipe pressure that is an intake pipe pressure on a boundary between a region where the amount of fresh air flowing in through said intake valve decreases when the valve timing of said intake valve is fixed and the length of the valve overlap period increases and a region where the amount of fresh air flowing in through said intake valve increases when the valve timing of said intake valve is fixed and the length of the valve overlap period increases; reference intake pipe pressure obtaining means that obtains the reference intake pipe pressure for the valve timing of said intake valve based on the information stored in said storing means; and blow-by determining means that determines the presence or absence of blow-by of fresh air into an exhaust side based on a result of comparison between the intake pipe pressure detected or estimated by said intake pipe pressure obtaining means and the reference intake pipe pressure obtained by said reference intake pipe pressure obtaining means.