PURPOSE: To securely detect a cylinder where misfire has occurred.

CONSTITUTION: In a multi-cylinder internal combustion engine where at least a half of an explosion cycle of each cylinder overlaps at least a half of a cylinder where next ignition is to occur, elapsed time T required for a crank shaft to rotate by a constant crank angle is detected. A deviation ΔT (=Tn-Tn-1) of elapsed time Tn at the time of combustion of a cylinder differs in an explosion cycle from this cylinder by 180 crank angle and elapsed time Tn-2 at the time of combustion of another cylinder where two cycles or more of the explosion from this cylinder is calculated. When the deviation ΔT exceeds a set value K, misfire is determined to be occurring in said another cylinder.