A separation device having high separation efficiency and a method for manufacturing a water absorption material using the separation device are provided. A separation device (1) includes a shredding unit (10), a beating unit (20), and a separation unit (30). The shredding unit (10) shreds a disposable diaper (processing target) containing a plastic (first material) and a water-absorbent polymer (second material) adhering to the plastic. The beating unit (20) beats the disposable diaper shredded by the shredding unit (10) with a beating member (22), thereby promoting dissociation of the water-absorbent polymer from the plastic. The separation unit (30) rotates a drum (32) in a state in which the disposable diaper beaten by the beating unit (20) is accommodated therein, thereby separating the water-absorbent polymer passing through holes (32a) from the disposable diaper.