Two imaging optical systems are provided. The two imaging optical systems are configured to have a difference in a ghost appearance condition under the same imaging condition by differentiating at least one of the angle, the resolution, and the variation adjustment in production. In Step S1, images captured by the two imaging optical systems are stored. In Step S2, corresponding positions of each respective portion of a subject between the two imaging optical systems are obtained. In Step S3, images at the corresponding positions are compared with each other for determining a bright portion having a deviation in a luminance value, as a ghost portion. In this configuration, it is possible to accurately detect a ghost generation position on a real-time basis.