An anomaly detection device includes a processor configured to identify a path region in an image representing surroundings of a vehicle, the path region representing a host vehicle lane on which the vehicle is traveling, extract a feature indicating the condition of a road surface regarding the path region from the image by inputting the path region in the image into a feature extractor that has been trained to extract the feature, and detect an abnormal condition in which the vehicle is unable to travel normally on the host vehicle lane, when the feature is outside a normal range that is a tolerable range in which the vehicle is able to travel normally.