To provide a fixing device capable of stiffening rod-like or pipe-like various kinds of accessories such as a stair rail mounted to a mounting wall surface against extreme bending stress imposed on them, and of improving supporting stability to the mounting surface.

This device is provided with a partition part 2 formed on the opening end side of a mounting leg part 1B of the accessory 1 and having a female screw part 2A or a male screw part 13 at its center, and a washer 11 composed by protrusively forming the screw part 13 screwed into the screw part 2A of the partition part 2 at the center of one end face of a body part 12, or by forming the screw part 2A for screwing the screw part 13 of the partition part 2 at the center of the one end face of the body part 12 and by integrally forming a flange part 14 fixed to the mounting wall surface P on the other end face of the body part 12. The device is provided with a stepped part 13B formed integrally with the lower end corner part of the circumference of the flange part 14 for fitting a bracket cover 3 to the leg part 13, and an engaging projection part 3A formed on the inside circumference side of the bracket cover 3 so as to be engaged with and held by the stepped part 13B.