To provide a bolt removal-preventing unit capable of decreasing the number of components to be able to reduce production cost and possessed of high strength.

The unit comprises a base fitting 22 provided with a cylindrical wall 26 of an internal diametrical side accommodating a head C of a bolt A around a washer 25 provided with a shaft inserting hole 24 of the bolt A, and a cap fitting 23 provided with an end plate 29 for closing a peripheral wall 28 of an external diametrical side fitted into an inside of the cylindrical wall 26 and an one end side of the peripheral wall 28. Portions between each of slits 30 provided in the peripheral wall 28 of the cap fitting 23 are formed in elastic piece portions 31 and then there are provided, in outer surfaces of end portions of the elastic piece portions 31, catching piece portions 32 for engaging with an engaging groove 27 in a removal-preventing state from the engaging groove when the cap fitting 23 is inserted into an inside of the base fitting 22.