1. An imaging apparatus, comprising: an image sensor including a plurality of focus detection pixels for generating a focus detection image and a plurality of imaging pixels for generating a captured image in which a subject is captured, the plurality of focus detection pixels being arranged in a predetermined direction; and an interpolation unit configured to interpolate a pixel value in a position of a first focus detection pixel among the plurality of focus detection pixels, the interpolation being performed by combining, or selecting one of output from first interpolation processing in which interpolation is performed using a pixel value of an imaging pixel surrounding the first focus detection pixel, and output from second interpolation processing in which interpolation is performed using pixel values of a plurality of focus detection pixels neighboring the first focus detection pixel.