To provide an attaching device for a post in which the post for attaching optional parts such as a panel or a lighting equipment can be simply and firmly attached to the open end part of a fixed pipe and the minimum number of parts are employed without greatly changing a tension even when a cap is slightly unfastened.

An attaching device for a post comprises a support cap 4 fitted to the open end 8 of a fixing pipe and a pressing cap 5 screwed to the support cap 4. A shaft part 9 with a small diameter formed on the end of a post 3 passes through the central parts of the pressing cap 5 and the support cap 4. The end part of the shaft part 9 is fitted to the support hole 11 of the fixing plate 10 fixed to the fixing pipe to screw the pressing cap 5 to the support cap 4. Thus, a tension is applied to the outer peripheral surface of the shaft part 9 by a holding means provided in the support cap 4 or the pressing cap 5 to prevent a looseness.