Provided is an internal combustion engine control device for controlling an engine by detecting combustion characteristics in a manner robust against disturbance such as noises and with a simple configuration. To this end, an internal combustion engine control device (ECU12) according to the present embodiment is provided with: a rotation speed calculation unit 122a for calculating the crank rotation speed of an internal combustion engine (engine 1); an extremum timing calculation unit 122b for calculating the extremum timing of the crank rotation speed calculated by the rotation speed calculation unit 122a; and a combustion state estimation unit (combustion phase calculation unit 122c) for estimating a combustion state on the basis of the extremum timing of the crank speed calculated by the extremum timing calculation unit 122b.