An imaging abnormality diagnosis device includes one or more processors configured to: detect a lane line in an image of a road surface captured by a camera mounted on a vehicle; estimate a shape of a road on which the vehicle is traveling, based on an output of a detector mounted on the vehicle, the detector being other than the camera; and detect as a distorted area an area in the image where the shape of the road and a shape of the lane line do not coincide with each other.