To prevent erroneous determination as to misfire of an internal combustion engine even when a torque ripple phenomenon occurs in an electric motor of a hybrid vehicle.

A misfire determination device is applied to a hybrid vehicle including: an internal combustion engine having an output shaft connected to a drive shaft of the hybrid vehicle so as to be able to transmit torque; and an electric motor having a rotor connected to the drive shaft so as to be able to transmit torque and a stator. The misfire determination device performs misfire determination of the internal combustion engine based on fluctuation in the rotational speed of the output shaft of the internal combustion engine. The misfire determination device inhibits, when the rotor is substantially still with respect to the stator while torque is output from the electric motor to the drive shaft and the internal combustion engine is driven, misfire determination when a condition of a torque ripple phenomenon where the torque outputted from the electric motor continuously increases/decreases is established.