A fastening structure for fastening a metal component and a resin component to each other, wherein: the metal component includes an attaching portion; the resin component includes a coupling portion facing the attaching portion; and the fastening structure comprising a combined member in which the attaching portion and the coupling portion are fastened to each other, which is formed by combining a fastening member (41, 46) and an elastic member, the combined member being inserted in an elongated hole, the combined member permits relative displacement of the attaching portion and the coupling portion along a longitudinal direction of the elongated hole, permits relative displacement of the attaching portion and the coupling portion within a predetermined range along an axial direction of the fastening member (41, 46) through elastic deformation of the elastic member, and absorbs displacement of the resin component with respect to the metal component due to thermal expansion and contraction of the resin component; characterized in that the fastening member (41, 46) includes a fastening bolt and a nut; the fastening bolt is inserted in the attaching portion through the elongated hole formed in the coupling portion, and the nut is screwed to the fastening bolt so that the metal component and the resin component (30; 130) are fastened to each other; the fastening bolt includes a head and a neck, the neck extending from the head and being inserted in the elongated hole; the neck is formed as a square shaft so as not to rotate in the elongated hole; the elastic member is formed by a plate spring member, the elastic member being bent into a folded state to form a seat, which contacts the attaching portion, and a pressing part, which is pressed against the coupling portion; and the pressing part includes an insertion portion, through which the neck is inserted such that the elastic member does not rotate with respect to the neck. the metal component includes an attaching portion; the resin component includes a coupling portion facing the attaching portion; and the fastening structure comprising a combined member in which the attaching portion and the coupling portion are fastened to each other, which is formed by combining a fastening member (41, 46) and an elastic member, the combined member being inserted in an elongated hole, the combined member permits relative displacement of the attaching portion and the coupling portion along a longitudinal direction of the elongated hole, permits relative displacement of the attaching portion and the coupling portion within a predetermined range along an axial direction of the fastening member (41, 46) through elastic deformation of the elastic member, and absorbs displacement of the resin component with respect to the metal component due to thermal expansion and contraction of the resin component; characterized in that the fastening member (41, 46) includes a fastening bolt and a nut; the fastening bolt is inserted in the attaching portion through the elongated hole formed in the coupling portion, and the nut is screwed to the fastening bolt so that the metal component and the resin component (30; 130) are fastened to each other; the fastening bolt includes a head and a neck, the neck extending from the head and being inserted in the elongated hole; the neck is formed as a square shaft so as not to rotate in the elongated hole; the elastic member is formed by a plate spring member, the elastic member being bent into a folded state to form a seat, which contacts the attaching portion, and a pressing part, which is pressed against the coupling portion; and the pressing part includes an insertion portion, through which the neck is inserted such that the elastic member does not rotate with respect to the neck.