A fastening structure, comprising: a plate-shaped metal member that is formed with a first through-hole through which a fastener is inserted; a plate-shaped resin member that overlaps the metal member, that is formed with a second through-hole with a larger diameter than the first through-hole, and that is fastened to the metal member by the fastener; and a collar that is made of metal and includes a tube portion inserted into the second through-hole and formed with a third through-hole through which the fastener is inserted, and a flange portion disposed facing the resin member in a state in which the tube portion has been inserted into the second through-hole; and an elastic member that is integrally provided at the collar, that is disposed between the flange portion and the resin member, and that covers an outer peripheral face of the flange portion and a lower face that is a face of the flange portion facing the resin member, characterized in that: on the elastic member, a press-contact portion is provided that projects toward a side of the resin member and is press-contacted against the resin member in a state in which the resin member has been fastened to the metal member by the fastener, on the collar, a projection portion that projects toward the resin member side at a position of the flange portion facing the resin member and that has a leading end portion formed in a bulge-shape bulging toward a side of the resin member, is formed on the lower face of the flange portion, and the press-contact portion and the projection portion are provided at positions that overlap with each other as viewed from a direction in which fastening force due to the fastener acts. a plate-shaped metal member that is formed with a first through-hole through which a fastener is inserted; a plate-shaped resin member that overlaps the metal member, that is formed with a second through-hole with a larger diameter than the first through-hole, and that is fastened to the metal member by the fastener; and a collar that is made of metal and includes a tube portion inserted into the second through-hole and formed with a third through-hole through which the fastener is inserted, and a flange portion disposed facing the resin member in a state in which the tube portion has been inserted into the second through-hole; and an elastic member that is integrally provided at the collar, that is disposed between the flange portion and the resin member, and that covers an outer peripheral face of the flange portion and a lower face that is a face of the flange portion facing the resin member, characterized in that: on the elastic member, a press-contact portion is provided that projects toward a side of the resin member and is press-contacted against the resin member in a state in which the resin member has been fastened to the metal member by the fastener, on the collar, a projection portion that projects toward the resin member side at a position of the flange portion facing the resin member and that has a leading end portion formed in a bulge-shape bulging toward a side of the resin member, is formed on the lower face of the flange portion, and the press-contact portion and the projection portion are provided at positions that overlap with each other as viewed from a direction in which fastening force due to the fastener acts. on the elastic member, a press-contact portion is provided that projects toward a side of the resin member and is press-contacted against the resin member in a state in which the resin member has been fastened to the metal member by the fastener, on the collar, a projection portion that projects toward the resin member side at a position of the flange portion facing the resin member and that has a leading end portion formed in a bulge-shape bulging toward a side of the resin member, is formed on the lower face of the flange portion, and the press-contact portion and the projection portion are provided at positions that overlap with each other as viewed from a direction in which fastening force due to the fastener acts.