Internal Combustion Engine Control Device

To accurately estimate a combustion state even in a case where the combustion state in a combustion chamber greatly changes. According to an aspect of the present invention, an internal combustion engine control device includes a rotational speed calculation unit that calculates a crank rotational speed of an internal combustion engine, an extreme value timing calculation unit that calculates an extreme value timing at which the crank rotational speed calculated by the rotational speed calculation unit becomes an extreme value, a combustion-state-calculation-means selection unit that selects combustion state calculation means for calculating a combustion state in a combustion chamber based on an operation state of the internal combustion engine, and a combustion state estimation unit that estimates the combustion state in the combustion chamber from the extreme value timing of the crank rotational speed by using the combustion state calculation means selected by the combustion-state-calculation-means selection unit