A crank angle sensor that outputs a crank angle signal at a predetermined crank angle by synchronizing rotation of a signal rotor fixed on a crank shaft of an internal combustion engine, an interval of the crank angle signals being longer at a specific crank angle corresponding to a position of a crank position reference part of the signal rotor, includes a backward rotation detecting function that outputs different crank angle signals in a forward rotation of the crank shaft and in a backward rotation of the crank shaft, and a control part disallows the detection of the crank position reference part when a stop request to the internal combustion engine is generated or when the backward rotation of the crank shaft is detected based on the crank angle signal, and controls the internal combustion engine by calculating the crank angle based on the crank angle of the crank position reference part detected before the detection of the crank position reference part is disallowed and the crank angle signal.