A misfire detection device executes a deactivating process that deactivates combustion control for air-fuel mixture in one or some of cylinders and a deactivating process that determines whether a misfire has occurred. The determining process determines whether a misfire has occurred by evaluating a magnitude of a rotation fluctuation amount using a determination value independent from the rotation fluctuation amount. The determining process includes a deactivation-related setting process that sets a different determination value for each of first and second cylinders when the deactivating process is executed. The deactivating process has not been executed in the first and second cylinders. The rotation fluctuation amount is a change amount of an instantaneous speed variable. The instantaneous speed variable indicates a speed in a case in which a crankshaft rotates in a rotation angle region that is less than or equal to an occurrence interval of a compression top dead center.