An internal combustion engine control apparatus includes an in-cylinder pressure sensor for detecting in-cylinder pressure. A combustion start time and combustion end time, which are parameters serving as control indexes for an internal combustion engine, are determined in accordance with ignition timing. Information about a heat release amount is acquired in accordance with the in-cylinder pressures that are measured at two points by the in-cylinder pressure sensor. The in-cylinder pressure is estimated in accordance with a relationship among the heat release amount information, control index parameters, and in-cylinder pressure.