[Problem] A separation device having a high separation efficiency is provided. [Solution] A separation device 1 includes a shredding unit 30 (first shredding unit), a separation unit 40 (first separation unit), and a ridge 44 (first ridge). The shredding unit 30 shreds a disposable diaper (processing target) containing a plastic (first material) and a water-absorbent polymer (second materials) adhering to the plastic into fragments. The separation unit 40 rotates a drum 42 in a state in which the disposable diaper fragments shredded by the shredding unit 30 are accommodated therein, thereby separating the water-absorbent polymer passing through holes 42a from the disposable diaper fragments. The ridge 44 is provided on an inner circumferential surface of the drum 42, and extends in a direction in which the central axis of the drum 42 extends.