FOCUS POSITION DETECTION DEVICE, FOCUS POSITION DETECTION METHOD, AND COMPUTER PROGRAM FOR FOCUS POSITION DETECTION

A focus position detection device calculates, for each shift amount calculation area contained in a measurement area defined on an image sensor, a local shift amount representing a shift between a first sub-image generated from first pixels and a second sub-image generated from second pixels and its confidence score, and corrects the confidence score based on at least one of the spacing between the first pixels, the spacing between the second pixels, and the amount of positional displacement between the first and second pixels in a direction orthogonal to the edge direction of a subject captured in the shift amount calculation area. Then, the focus position detection device calculates a representative value representing the distance between the image sensor and the focus position, by taking a weighted average of the local shift amounts of the respective shift amount calculation areas with weighting based on the corrected confidence scores.