An engine misfire detection apparatus of detecting a misfire of an internal combustion engine in a power output apparatus that includes the internal combustion engine having an output shaft linked to a driveshaft and a motor enabling input and output of power from and to the output shaft of the internal combustion engine and ensures output of at least part of output power of the internal combustion engine to the driveshaft under vibration control of controlling the motor to reduce a vibration caused by operation of the internal combustion engine, the engine misfire detection apparatus comprising: a rotational position detector that detects a rotational position of the output shaft of the internal combustion engine; a unit angle rotation time calculator that computes a unit angle rotation time required for rotation of the output shaft of the internal combustion engine by every predetermined unit rotation angle according to the detected rotational position; an air-fuel ratio detector that measures an air-fuel ratio as a ratio of a fuel to the air supplied to the internal combustion engine, an engine misfire tentative detection module that makes tentative detection on occurrence or non-occurrence of a misfire in the internal combustion engine based on the computed unit angle rotation time; a first engine misfire final detection module that, in response to the tentative detection of a misfire in the internal combustion engine by the engine misfire tentative detection module, makes final detection on the occurrence or the non-occurrence of a misfire in the internal combustion engine based on the computed unit angle rotation time and the measured air-fuel ratio, wherein the first engine misfire final detection module makes no final detection of a misfire in the internal combustion engine when the measured air-fuel ratio is out of a specific range including a preset air-fuel ratio; and a second engine misfire final detection module that, in the event of no final detection of a misfire in the internal combustion engine by the first engine misfire final detection module, outputs prohibition of execution of the vibration control and, after the prohibition of execution of the vibration control, makes final detection on the occurrence or the non-occurrence of a misfire in the internal combustion engine based on the computed unit angle rotation time. a rotational position detector that detects a rotational position of the output shaft of the internal combustion engine; a unit angle rotation time calculator that computes a unit angle rotation time required for rotation of the output shaft of the internal combustion engine by every predetermined unit rotation angle according to the detected rotational position; an air-fuel ratio detector that measures an air-fuel ratio as a ratio of a fuel to the air supplied to the internal combustion engine, an engine misfire tentative detection module that makes tentative detection on occurrence or non-occurrence of a misfire in the internal combustion engine based on the computed unit angle rotation time; a first engine misfire final detection module that, in response to the tentative detection of a misfire in the internal combustion engine by the engine misfire tentative detection module, makes final detection on the occurrence or the non-occurrence of a misfire in the internal combustion engine based on the computed unit angle rotation time and the measured air-fuel ratio, wherein the first engine misfire final detection module makes no final detection of a misfire in the internal combustion engine when the measured air-fuel ratio is out of a specific range including a preset air-fuel ratio; and a second engine misfire final detection module that, in the event of no final detection of a misfire in the internal combustion engine by the first engine misfire final detection module, outputs prohibition of execution of the vibration control and, after the prohibition of execution of the vibration control, makes final detection on the occurrence or the non-occurrence of a misfire in the internal combustion engine based on the computed unit angle rotation time.