1. A focus control amount determination apparatus, comprising: a detection means for detecting a predetermined structure within a subject from inputted image data obtained through digital conversion of an image of the subject generated on an imaging surface, formed of an image sensor, by focusing the light from the subject through an imaging optical system; a parameter obtaining means for obtaining a sharpness parameter that represents a weighting value for a statistical characteristic amount representing a sharpness level of the structure by applying the structure detected by the detection means to a model, which represents the structure by means of: one or more statistical characteristic amounts, including the statistical characteristic amount representing the sharpness level of the structure, obtained by performing a predetermined statistical processing on image data representing a plurality of images that represent the predetermined structure in different sharpness levels; and a weighting parameter for weighting each of the statistical characteristic amounts according to each of the characteristics of the structure; and a control amount determination means for determining the focus control amount for the imaging optical system such that the structure within the subject of the image is brought into focus according to the obtained value of the sharpness parameter.