A fastening structure that includes: a nut fabricated of metal that is screwed onto the threaded portion; a collar including a collar main body fabricated of metal that includes: a tubular portion through which the threaded portion penetrates, and a flange that is formed at an outer periphery portion of the tubular portion and that is disposed at the other plate thickness direction side of the resin member, the collar main body touching against the washer main body and the nut; and a base portion fabricated of resin that structures a portion of the collar and that is disposed between the flange and the resin member.