Disclosed herein is a method for operating an apparatus for generating an all-in-focus image. The method may include generating a focus-map-calculating model through deep learning for images having different focuses and a reference all-in-focus image corresponding thereto, calculating a focus map for each of multi-focus images, which are captured by a camera, using the focus-map-calculating model, and generating an all-in-focus image for the multi-focus images using the focus map.