A hole plug which includes a flange part which covers an opening peripheral surface of an attachment hole formed on an attachment member at a predetermined inclined angle against the opening peripheral surface and a cylindrical outer peripheral wall part formed to extend downward from an inner edge part of the flange part. A flange part associating bending part is formed as a base point in order for bending an upper part of an outer peripheral wall part of the hole plug from a predetermined position of the outer peripheral wall part in a direction away from a hole edge when a tip of a flange part is contacted with an opening peripheral surface of the attachment member. Thus, the hole plug can reduce an insertion load, corresponding to variation of a plate thickness, and maintain a water sealing property.