To visually ascertain the tightening states of a bolt and nut from the front side of the head side of the bolt or the nut side by positioning the ring plate-like elastic material, which is directly pressed by the head section of the bolt or the face of the nut, in front of a washer and fitting the ring plate-like elastic material in a state of directly covering to the bolt.

A fastening ascertaining tool A is provided with a washer 30 having a fastening state judging face 32 provided so as to surrounded a hole 31, into which a bolt is inserted, and a ring plate-like elastic material 40, which is used secured and attached to the side of the judging face 32 in the washer 30 and has a smaller annex face than that of the fastening judging face 32. In fastening an object B to be attached to, the ring plate-like elastic material 40 and washer 30 are laid on one on top of the other and mounted on a bolt 10 with the ring plate-like elastic material 40 of the fastening ascertaining tool A put outside, and in fastening the bolt 10 or nut 20, the swelling section 41 of the ring plate-like elastic material 40' swelling along the fastening judging face 32 of the washer 30 is constituted so as to be visible.