To prevent protrusion of an adhesive when a bolt is screwed in a cap nut coated with an adhesive for locking.

Fastening structure for a cap nut and a bolt comprises a first member 3 having a cap nut part 7 having a screw hole 5 formed in a bag-form state; a second member 1 formed in a through-hole 11; a bolt 13 extending through the through-hole 11 and threadably attached in the screw hole 5 coated with an adhesive for locking and fixing the first and second members 3 and 1; and a filling member 15 arranged in a space 17 formed between the tip side of the bolt 13 and the bottom of a bag-form screw hole 5 to reduce its volume.