Misfire Determination Device for Multi-Cylinder Four-Cycle Engine

A misfire determination device for a multi-cylinder four-cycle engine (11), which determines a misfire based on a pulse (P) outputted each time when a crankshaft (15) rotates by a predetermined rotational angle, includes a timing device (30) for timing an elapsed time (T) until a number of pulses in a stroke (TN) are counted at each pulse output timing, a deviation calculating device (30) for calculating a deviation (DT) between a first time (TR) and a second time (TL), an integrated value calculating device (30) for calculating an integrated value (RC) by integrating the calculated deviation by the predetermined rotational angle of the crankshaft, and a determining device (30) for determining whether or not the misfire occurs at any one of the plurality of the cylinders (12) based on a magnitude relationship between the integrated value and a predetermined threshold value (DR).