In an internal combustion engine having an in-cylinder pressure sensor provided on each cylinder, an in-cylinder pressure detection value is corrected into an absolute pressure using an absolute pressure correction value Pr by calculating the absolute pressure correction value Pr (=(P2V2κ−P1V1κ)/(V1κ−V2κ)) from in-cylinder pressure detection values P1 and P2, in-cylinder volumes V1 and V2, and a specific heat ratio K at predetermined crank angles θ1 and θ2 during the adiabatic compression stroke from IVC to the ignition timing. When the adiabatic compression stroke (ignition timing−IVC) is shorter than a predetermined crank angle period CAth, the ignition timing is delayed. When the adiabatic compression stroke is longer than or equal to CAth, IVC is advanced. Preferably, a torque variation is suppressed by controlling the ignition timing of each cylinder before IVC is advanced.