PURPOSE: To provide an inexpensive resin nut that has a locking function and does not damage a work.

CONSTITUTION: A nut part 1 provided with a tool engagement part 2 on its outer circumferential face is formed from a resin material and the resin nut 1 is provided with a screwless hole 5 whose inside diameter is smaller than the outside diameter of the thread of a screw to threadly inserted in the center of the nut part 1 and larger than the root diameter. The screwless hole of resin material is thus smaller than the screw outside diameter so that thread is formed in this screwless hole by a screw or a bolt in fastening and loosening of the screw can be prevented by receiving elastic restitutive force from the outside face of the resin caused by elasticity of the resin material. Because the nut 1 is made of resin, it can lighten a work assembled thereby, improve assemble workability, reduce cost, and prevent a lens, a resin board, an exterior material, etc., from being damaged.