An imaging unit is configured to capture images of a subject. A sensor is configured to detect brightness. A first detector is configured to detect whether or not a period during which a predetermined brightness has been detected by the sensor continues for a first period of time. A second detector is configured to detect whether or not a period during which the predetermined brightness has been detected by the sensor continues for a second period of time shorter than the first period of time. A determiner is configured to determine a circumstance where the imaging unit captures images of the subject in a daytime in a specific state where light is temporarily cut off, based on a first detection result by the first detector and a second detection result by the second detector.