Abstract: A knockdown cable tray made of a fire-retardant plastic and a coupling device therefor are capable of being used to easily and efficiently install an incombustible knockdown cable tray to suspend a plurality of cables from a ceiling. The knockdown cable tray includes: a pair of side panels, each of which includes a frame having a plurality of coupling holes formed in opposite ends thereof in a lengthwise direction and a coupler protruding outwardly from the frame, the side panels being located opposite each other; a plurality of rung members, each of which is detachably coupled to the couplers and firmly supports the side panels; and coupling devices, each of which is detachably coupled to the coupling holes of each frame and firmly couples a plurality of side panels disposed in a lengthwise direction.