A fastening structure for fastening an attaching member to an attached member comprising: a bolt having a head portion and a threaded portion integrally formed with the head portion; a bottomed tubular bolt cover having an opening end; and a cap member accommodated in the bolt cover and closing the opening end of the bolt cover, the cap member includes a first engagement portion formed thereon; wherein the bolt cover includes: a bottom portion abutting on a bottom surface of the bolt, the bottom portion having a through bore formed therein and configured to have the threaded portion of the bolt pass through, and a grip portion projecting from an outer circumference of the bottom portion and surrounding a periphery of the head portion of the bolt, the grip portion having a second engagement portion configured to engage with the first engagement portion and constituted by a plurality of protrusions inwardly projecting from an inner peripheral portion of the grip portion of the bolt cover; wherein the bolt is prevented from being rotated in a direction to remove the bolt, and the bottom portion of the bolt cover is interposed between the bottom surface and the attaching member in a state that the attaching member is fastened to the attached member via the fastening structure; characterized in that: the head portion of the bolt is provided with a flange portion radially outwardly protruding from the head portion of the bolt; and the flange portion of the bolt is made to catch the second engagement portion of the bolt cover as the bolt is moved towards the opening end of the bolt cover, so that the bolt is integrated with the bolt cover in a state that the cap member is not accommodated in the bolt cover. a bolt having a head portion and a threaded portion integrally formed with the head portion; a bottomed tubular bolt cover having an opening end; and a cap member accommodated in the bolt cover and closing the opening end of the bolt cover, the cap member includes a first engagement portion formed thereon; wherein the bolt cover includes: a bottom portion abutting on a bottom surface of the bolt, the bottom portion having a through bore formed therein and configured to have the threaded portion of the bolt pass through, and a grip portion projecting from an outer circumference of the bottom portion and surrounding a periphery of the head portion of the bolt, the grip portion having a second engagement portion configured to engage with the first engagement portion and constituted by a plurality of protrusions inwardly projecting from an inner peripheral portion of the grip portion of the bolt cover; wherein a bottom portion abutting on a bottom surface of the bolt, the bottom portion having a through bore formed therein and configured to have the threaded portion of the bolt pass through, and a grip portion projecting from an outer circumference of the bottom portion and surrounding a periphery of the head portion of the bolt, the grip portion having a second engagement portion configured to engage with the first engagement portion and constituted by a plurality of protrusions inwardly projecting from an inner peripheral portion of the grip portion of the bolt cover; wherein the bolt is prevented from being rotated in a direction to remove the bolt, and the bottom portion of the bolt cover is interposed between the bottom surface and the attaching member in a state that the attaching member is fastened to the attached member via the fastening structure; characterized in that: the head portion of the bolt is provided with a flange portion radially outwardly protruding from the head portion of the bolt; and the flange portion of the bolt is made to catch the second engagement portion of the bolt cover as the bolt is moved towards the opening end of the bolt cover, so that the bolt is integrated with the bolt cover in a state that the cap member is not accommodated in the bolt cover. the head portion of the bolt is provided with a flange portion radially outwardly protruding from the head portion of the bolt; and the flange portion of the bolt is made to catch the second engagement portion of the bolt cover as the bolt is moved towards the opening end of the bolt cover, so that the bolt is integrated with the bolt cover in a state that the cap member is not accommodated in the bolt cover.