The coupling apparatus for structural members includes a paired couplers for coupling structural members with each other, and each coupler includes a cylindrical main body, engaging projections spaced apart from each other at predetermined intervals in a circumferential direction at an end of the body and projecting along the center line of the body, and engaging hooks projecting in one circumferential direction at the projecting end portions of the projections. At least one coupler further includes a coupling direction changing mechanism which couples the at least one coupler with a predetermined position of a structural member corresponding thereto so that the center line of the body of the at least one coupler can be orientated in a desired direction.