A misfire detection device for an internal combustion engine including a crankshaft mechanically connected to a motor generator includes a storage device and processing circuitry. The storage device stores mapping data. The mapping data is data specifying a mapping that outputs a misfire variable using a rotation waveform variable and a damping variable as an input. The misfire variable is a variable related to a probability that a misfire has occurred. The rotation waveform variable is a variable including information on a difference between values of instantaneous speed corresponding to short angular intervals differing from each other. The damping variable is a variable related to a state of a damping process that controls a torque of the motor generator to reduce vibration of a power transmission system of a vehicle.