A control apparatus for an internal combustion engine, comprising: an in-cylinder pressure sensor detecting in-cylinder pressure; the control apparatus being characterized by further comprising: obtaining means for obtaining an in-cylinder-pressure-maximum crank angle (θ Pmax) when in-cylinder pressure detected by the in-cylinder pressure sensor becomes maximum during a combustion duration; and absolute pressure correction means for setting, using the in-cylinder-pressure-maximum crank angle as a baseline, a first crank angle (θ 1) and a second crank angle (θ 2) on a retard side of the first crank angle in an adiabatic compression stroke from a closing timing of an intake valve until a start of combustion and, based on in-cylinder pressure and in-cylinder volume at each of the first crank angle (θ 1) and the second crank angle (θ 2), performing absolute correction for the in-cylinder pressure detected by the in-cylinder pressure sensor, wherein: the second crank angle (θ 2) that is set by the absolute pressure correction means is a crank angle set in advance with respect to the in-cylinder-pressure-maximum crank angle (θ Pmax) in a manner so as to be a timing in the adiabatic compression stroke on a retard side with respect to the spark timing, and is used for the absolute correction; the first crank angle (θ 1) is advanced with respect to the second crank angle (θ 2) by a predetermined crank angle interval (Δθ); and the first crank angle (θ 1) and the second crank angle (θ 2) are changed in accordance with the in-cylinder-pressure-maximum crank angle (θ PMAX). an in-cylinder pressure sensor detecting in-cylinder pressure; the control apparatus being characterized by further comprising: obtaining means for obtaining an in-cylinder-pressure-maximum crank angle (θ Pmax) when in-cylinder pressure detected by the in-cylinder pressure sensor becomes maximum during a combustion duration; and absolute pressure correction means for setting, using the in-cylinder-pressure-maximum crank angle as a baseline, a first crank angle (θ 1) and a second crank angle (θ 2) on a retard side of the first crank angle in an adiabatic compression stroke from a closing timing of an intake valve until a start of combustion and, based on in-cylinder pressure and in-cylinder volume at each of the first crank angle (θ 1) and the second crank angle (θ 2), performing absolute correction for the in-cylinder pressure detected by the in-cylinder pressure sensor, wherein: the second crank angle (θ 2) that is set by the absolute pressure correction means is a crank angle set in advance with respect to the in-cylinder-pressure-maximum crank angle (θ Pmax) in a manner so as to be a timing in the adiabatic compression stroke on a retard side with respect to the spark timing, and is used for the absolute correction; the first crank angle (θ 1) is advanced with respect to the second crank angle (θ 2) by a predetermined crank angle interval (Δθ); and the first crank angle (θ 1) and the second crank angle (θ 2) are changed in accordance with the in-cylinder-pressure-maximum crank angle (θ PMAX). obtaining means for obtaining an in-cylinder-pressure-maximum crank angle (θ Pmax) when in-cylinder pressure detected by the in-cylinder pressure sensor becomes maximum during a combustion duration; and absolute pressure correction means for setting, using the in-cylinder-pressure-maximum crank angle as a baseline, a first crank angle (θ 1) and a second crank angle (θ 2) on a retard side of the first crank angle in an adiabatic compression stroke from a closing timing of an intake valve until a start of combustion and, based on in-cylinder pressure and in-cylinder volume at each of the first crank angle (θ 1) and the second crank angle (θ 2), performing absolute correction for the in-cylinder pressure detected by the in-cylinder pressure sensor, wherein: the second crank angle (θ 2) that is set by the absolute pressure correction means is a crank angle set in advance with respect to the in-cylinder-pressure-maximum crank angle (θ Pmax) in a manner so as to be a timing in the adiabatic compression stroke on a retard side with respect to the spark timing, and is used for the absolute correction; the first crank angle (θ 1) is advanced with respect to the second crank angle (θ 2) by a predetermined crank angle interval (Δθ); and the first crank angle (θ 1) and the second crank angle (θ 2) are changed in accordance with the in-cylinder-pressure-maximum crank angle (θ PMAX). the second crank angle (θ 2) that is set by the absolute pressure correction means is a crank angle set in advance with respect to the in-cylinder-pressure-maximum crank angle (θ Pmax) in a manner so as to be a timing in the adiabatic compression stroke on a retard side with respect to the spark timing, and is used for the absolute correction; the first crank angle (θ 1) is advanced with respect to the second crank angle (θ 2) by a predetermined crank angle interval (Δθ); and the first crank angle (θ 1) and the second crank angle (θ 2) are changed in accordance with the in-cylinder-pressure-maximum crank angle (θ PMAX).