A rotary drum for a fiber-stacking device includes a drum body, pattern plates each having a single fiber-stacking depression, and holding mechanisms each detachably holding a corresponding pattern plate on the outer circumferential surface of the drum body. Each holding mechanism has a fixed hook and a moveable hook. The fixed hook is immovably attached to one side of the drum body and forms a first groove with the drum body. The movable hook is attached to the other side of the drum body to be moveable between a holding position and a release position, forms a second groove with the drum body at the holding position, and opens the second groove at the release position. When the movable hook is at the holding position, the two side parts of the pattern plate are accommodated inside the first and second grooves.