PROBLEM TO BE SOLVED: To realize a proper autofocus at a small load irrespective of a number of a target of focus or a fluctuation of a position.SOLUTION: An autofocus device of an imaging system comprises an evaluation value calculation part and a focusing position determination part. The evaluation value calculation part calculates an evaluation value for determining a focusing position in each image data obtained by imaging a subject at a focal position. The focusing position determination part determines the focusing position on the basis of the evaluation value of a plurality of focal positions. The evaluation value calculation part generates evaluation data contributed by a positive weight to a first score component and contributed by a negative weight to a second score component by using the first score component calculated for a first region which has the size including a target and the second score component calculated to a second region which has the size including a peripheral part of the target in each local area of image data, and calculates the evaluation value on the basis of the evaluation data in the plurality of local regions.SELECTED DRAWING: Figure 3
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