To solve the problems on a conventional removal preventing fastener which is complicated and large in size, that it is uneconomical and inferior in beautiful appearance.

The removal preventing fastener comprises a cap body 1 consisting of a capped upper face 3 having an internal space large enough to cover a nut or a bolt head portion and a peripheral wall 4 suspended down from the upper face 3 and having a through-hole 5 in the upper face 3 at its central portion, a plurality of latching pawls 6 bent inside and provided at the lower end of the peripheral wall 4, and a proper length of cut groove 7 arranged in the peripheral wall near the pawl in a range from the lower end to the upper face, and a supporting washer body 2 having a through-hole 9 in a plate seat face 8 at its central portion and a protruded portion 10 rising higher than the seat face with an inner peripheral portion of the through-hole bent almost 90° from the seat face.