To provide a screw unit for attachment-cum-fastening providing fastening of an object and attachment of another object to its fastening portion, and a screw module for attachment-cum-fastening mounting a portable apparatus such as an illumination apparatus to the fastening portion.

The screw unit for attachment-cum-fastening includes a shaft part including a male screw part 3, a screw for fastening having a head 4 added to a rear end of the shaft part and a female screw part recessed on the head, and a screw for attachment having a shaft part including a male screw part screwed into a female screw part and a head added to a rear end of the shaft part. It is favorable to form the shaft part of the screw for fastening and the female screw part on the same axis. It is preferable that a pitch or a screw diameter of the male screw part of the screw for fastening is formed smaller than the male screw part of the screw for attachment, and a length of the male screw part of the screw for fastening is formed larger than the male screw part of the screw for attachment. It is favorable to have a latching hole for rotation on a bottom of the female screw part in the head of the screw for fastening.