An apparatus for retraining an object detector according to an exemplary embodiment includes an inputter configured to receive an undetected image, a style transferer configured to generate one or more first augmented images that have the same content attribute as an object area of the undetected image, but a different style attribute, a content transferer configured to generate one or more second augmented images that have the same style attribute as the object area, but a different content attribute, and an influence analyzer configured to analyze a cause of non-detection of the undetected image by comparing object detection reliabilities of the undetected image, the first augmented image, and the second augmented image.