A hole plug attachment structure includes: a first attachment-target member is formed with a first attachment hole; a second attachment-target member is formed with a second attachment hole; and a hole plug that includes a tube-shaped outer peripheral wall, a blocking portion, a ring shaped flange jutting out toward a radial direction outer side of the outer peripheral wall from an end portion of the outer peripheral wall on an opposite side from an insertion direction so as to cover a location surrounding the second attachment hole, and a hook portion, a location of the flange that abuts an edge of the second attachment hole being thicker than a location of the flange that abuts the edge of the first attachment hole, in a state in which a back face of the flange abuts both the edge of the first attachment hole and the edge of the second attachment hole.