A control apparatus for a multi-cylinder internal combustion engine includes pressure sensors used for acquiring combustion chamber pressure data for each engine cylinder, during each of a series of selection intervals respectively corresponding to that cylinder, with each selection interval corresponding to a specific angular displacement of the crankshaft and having a timing determined with respect to a reference piston position in the corresponding cylinder. The timing of the selection intervals is adjusted in accordance with current conditions of the engine, such as a fuel injection mode, to be appropriate for monitoring combustion conditions in the cylinders.