To prevent damage from being easily generated of a screw hole in a structure mounting a resin-made part by a tapping screw with a frame, cover, etc., of an image forming device serving as a mate part.

A U-groove 22 and an angle part 23 inserting a screw are formed in a protrusion 21 of a cover 20 in an image forming device. A hole 27 inserting a screw 26 is provided in an upper surface of a resin member 25 mounted in the cover 20, and a pair of ribs 28, 28 are formed in a lower surface, so that an elastic member 30 can be positioning held between the ribs 28 and 28 by the screw 26. The elastic member 30, provided with an internal thread part 31 in a position corresponding to the hole 27 of the resin member 25, makes the screw 26 screw in. The protrusion 21 is inserted in a clearance between the resin member 25 and the elastic member 30, the screw 26 is made to advance in the U-groove 22 and tighten the screw 26 from a condition thereof, the elastic member 30 is deformed and made in adhesion to the protrusion part 21, so as to fix the resin member 25 to the cover 20.