Abstract: A misfire detecting method is provided for preventing erroneous detection by prohibiting misfire detection when it is judged that an internal combustion engine is operating in a particular operating condition in which load on the engine can suddenly change, wherein a processor for repeatedly executing a misfire detection process immediately ends the present cycle of the misfire detection process when it is judged that the engine has just been started (S3), when it is judged that the igniton key has just been turned off (S4), or when it is judged that the engine is decelerating, that the transmission is performing a shift operation, or that the vehicle is running on a rough road (S5-7), to thereby avoid erroneous detection which is liable to occur during rough-road travel etc.