A method of and an apparatus for detecting the maximum cylinder pressure angle in an internal combustion engine. The method comprises the steps of measuring the time lapse required for the engine crankshaft to pass between a reference crankshaft angle such as TDC and the crankshaft angle at which the cylinder pressure becomes maximum and multiplying the measured time lapse by a time-angle conversion factor. The rate of change in the engine rotation speed is taken into consideration in carrying out the time-angle conversion so that it is possible to accurately determine the position at which the cylinder pressure becomes maximum in terms of crankshaft angle regardless of the operating condition of the engine. In the apparatus, the engine speed change rate is also compensated. The time-angle conversion can be carried out accurately even when there is used a crankshaft angle sensor which detects the crankshaft angle at relatively large intervals such as once every 30 degrees.