A focusing auxiliary device of an image-capturing apparatus includes a base and an extension rod. The base is arranged on the image-capturing apparatus. The extension rod is coupled to and movable relative to the base for sustaining against a supporting surface so as to keep the lens set of the image-capturing apparatus at a fixed distance from an object to be photographed. By marking graduations on the extension rod, the focusing distance from the image-capturing apparatus to the object can be realized at the same time.