Misfire detection device and method for internal combustion engine

A misfire detection device for an internal combustion engine, the internal combustion engine including a sensor and cylinders, wherein

• the misfire detection device is configured to execute:
• a deactivating process that deactivates combustion control for air-fuel mixture in one or some of the cylinders;
• a provisional determination process that uses a detection value of the sensor to output a logical value indicating whether a misfire has occurred;
• a provisional determination counting process that counts a number of times a specific one of the logical value output by the provisional determination counting process has been output;
• and
• an official determination process that makes an official determination of whether the misfire has occurred using, as an input, the number of times counted by the provisional determination counting process during a specific period,
• a length of the specific period is defined by a number of rotations of a crankshaft of the internal combustion engine,
• the official determination process includes a process that makes the official determination that the misfire has occurred even in a case where a frequency at which the provisional determination of the misfire has been made in the specific period is lower when the deactivating process is executed in the specific period than when the deactivating process is not executed in the specific period, and
• the frequency at which the provisional determination of the misfire has been made in the specific period is a value obtained by dividing a number of times the provisional determination has been made by the number of rotations of the crankshaft in the specific period.