1. An automatic focusing method, executed in an image capturing device, comprising: through multiple cameras of the image capturing device, capturing a scene, so as to obtain multiple images generated corresponding to the cameras, wherein the scene comprises a single one object or multiple objects; generating multiple depth maps according to the images, wherein each of the depth map is generated according to the arbitrary two images, and the depth map has depth information of the single one object or at least one of the multiple objects, or does not have the depth information of the single one object or all of the multiple objects; according to resolutions of the single one or the multiple objects in the depth maps, selecting the depth information of the single one or the multiple objects in the depth maps to generate a merged depth map; according to the merged depth map, calculating a target focus distance of the single one object or target focus distances of the multiple objects; and according to the target focus distance of the single one object or one of the target focus distances of the multiple objects, adjusting an actual focus distance of the multi-lenses module associated with the cameras.