A failure diagnosis apparatus comprises a controller that is configured to execute a failure diagnosis process of the internal combustion engine based on a predetermined diagnosis requirement. The diagnosis requirement in a case where engine-operation-electric-power supply is executed is made different from the diagnosis requirement in a case where engine-normal-operation is executed such that a failure of the internal combustion engine in the case where the engine-operation-electric-power supply is executed is less likely to be detected or the failure of the internal combustion engine is less likely to be recognized by a driver than in the case where the engine-normal operation is executed.