PROBLEM TO BE SOLVED: To accurately measure a blood flow from an SLO image group imaged in different focus positions.SOLUTION: Signal light is adjusted to a first focus position to take a first SLO image, and a second SLO image is taken by signal light adjusted to a second focus position deeper than the first focus position. A vascular territory is identified from the taken first SLO image, and information on a blood flow velocity of a blood vessel is identified from the taken second SLO image.
