PURPOSE: To decrease the number of parts used in a combusting condition monitoring device of a multi-cylinder internal combustion engine which senses misfire etc., and eliminate judgement dispersion cylinder to cylinder.

CONSTITUTION: Piezo type pressure sensors 3 installed cylinders of a multi- cylinder internal combustion engine are connected parallelly and put in connected with a charge amplifier 4. Thereby pressure signals are processed by a single abnormal combustion judging circuit 7. Judgement of cylinders with the pressure signals entered on time-series basis is made with a signal given by a crank angle sensor 5.