Abnormality detection device and abnormality detection method

An abnormality detection device for detecting occurrence of an abnormality of a lens of a camera, the abnormality detection device comprising:

• processing circuitry configured to
• calculate an index value indicating a sum of edge strengths in a second image that is an image captured by the camera for capturing a vehicle compartment at timing before a user enters a vehicle;
• calculate a differential value between an index value indicating a sum of edge strengths in a reference image, which is an image captured by the camera under an imaging condition equivalent to an imaging condition of a second image before the second image is captured, and the calculated index value;
• determine whether the differential value is equal to or greater than a threshold value;
• and
• output a visual or auditory warning indicating an abnormality has been detected in the lens of the camera in a case where it is determined that the differential value is equal to or greater than the threshold value.