A misfire detection device for an internal combustion engine includes processing circuitry. The internal combustion engine includes a selective reduction type catalyst configured to remove NOx from an exhaust gas, an addition valve arranged upstream of the catalyst to add a reducing agent into the exhaust gas, and a NOx concentration sensor arranged downstream of the catalyst to detect a downstream concentration, that is, a NOx concentration in the exhaust gas downstream of the catalyst. The processing circuitry is configured to execute an addition process adding the reducing agent into the exhaust gas with operation of the addition valve and a determination process determining that a misfire has occurred in the internal combustion engine when a detection value of the downstream concentration is decreased on condition that the addition process is being executed.