A measurement unit measures a first generation time of a first vanishing point of a plurality of radially diverging motion vectors generated in a front image region and a second generation time of a second vanishing point of a plurality of converging motion vectors generated in the front image region within a predetermined period of time in a state in which an image rotation unit adjusts positions of the front image region and a rear image region in a circumferential direction. The image rotation unit keeps the positions of the front image region and the rear image region in the circumferential direction when the first generation time measured by the measurement unit is longer than the second generation time, and rotates the captured image to reverse the front image region and the rear image region when the first generation time is not longer than the second generation time.