A coupling apparatus (40, 50) comprising an annular coupling body having a proximal end part attached to a predetermined part of an object to be connected and a distal end part positioned opposite the proximal end part; and plural fitting projections projecting along an axial direction of the coupling body from plural predetermined circumferential positions on the distal end part of the coupling body, each fitting projection having an engaging hook projecting in one predetermined circumferential direction at a projecting end part thereof, two (40, 40 or 50, 50) of the coupling apparatuses approaching coaxially each other to fit the fitting projections of one coupling apparatus into fitting recesses between the fitting projections of the other coupling apparatus, next, the coupling body of the one coupling apparatus being rotated in a predetermined circumferential direction relative to the coupling body of the other coupling apparatus to make the engaging hooks of the fitting projections of the one coupling apparatus engage with the engaging hooks of the fitting projections of the other coupling apparatus, thus detachably connecting the two coupling apparatuses (40, 40 or 50, 50)to each other, characterized in that the coupling body and the plural fitting projections are formed independently of each other, a fixing structure, which is independent of the coupling body and the fitting projections, detachably fixes the fitting projections to the predetermined circumferential positions on the distal end part of the coupling body, an outward overhang projecting outward in a radial direction of the coupling body is provided on the outer periphery of the distal end part of the coupling body adjacent to an end surface of the distal end part, each fitting projection has an inner periphery placed on a part of the outer periphery of the distal end part of the coupling body, the part being adjacent to the outward overhang in a side opposite to the end surface, and an outward tapering surface inclining toward the inner periphery with the outward tapering surface extending away from the projecting end part in the axial direction, when the inner peripheries of the plural fitting projections are placed on the outer periphery of the distal end part of the coupling body to be adjacent to the outward overhang, and the fixing structure is detachably fixed on a part of the outer periphery of the distal end part of the coupling body, the part being in a side of the outward overhang opposite to the plural fitting projections along the axial direction, the fixing structure has an inward tapering surface which fits the outward tapering surfaces of the plural fitting projections to fix the plural fitting projections coaxially on the predetermined positions of the outer periphery of the distal end part of the coupling body, and the fixing structure has a cutout exposing at least one outward tapering surface of the plural fitting projections the inner peripheries of which are placed on the outer periphery of the distal end part of the coupling body adjacent to the outward overhang, and the cutout allows at least one fitting projection the outward tapering surface of which is exposed in the cutout, to approach or be separated from the position on the outer periphery of the distal end part of the coupling body adjacent to the outward overhang through the cutout.