A manufacturing method of a water absorbing material comprising: an obtaining step of separating polyvinyl chloride from vinyl chloride wallpaper with a separation device to obtain paper; a granulating step of granulating a raw material containing the paper obtained in the obtaining step; and a coating step of coating a granule granulated in the granulating step with a coating material, wherein the separation device includes: a first shredding unit that shreds the vinyl chloride wallpaper; and a first separation unit that has a first tubular portion in which a large number of first holes that allow the polyvinyl chloride contained in the vinyl chloride wallpaper shredded by the first shredding unit to pass through without allowing the paper to pass through are formed, and that separates the polyvinyl chloride passing through the first holes from the vinyl chloride wallpaper by rotating the first tubular portion in a state in which the vinyl chloride wallpaper shredded by the first shredding unit is accommodated in the first tubular portion, and an inside of the first tubular portion is provided with a rotating rod that has a central axis coinciding with a central axis of the first tubular portion and is rotatable about the central axis, and a screw member that is helically provided around the rotating rod and has a plurality of teeth formed in the screw member. an obtaining step of separating polyvinyl chloride from vinyl chloride wallpaper with a separation device to obtain paper; a granulating step of granulating a raw material containing the paper obtained in the obtaining step; and a coating step of coating a granule granulated in the granulating step with a coating material, wherein the separation device includes: a first shredding unit that shreds the vinyl chloride wallpaper; and a first separation unit that has a first tubular portion in which a large number of first holes that allow the polyvinyl chloride contained in the vinyl chloride wallpaper shredded by the first shredding unit to pass through without allowing the paper to pass through are formed, and that separates the polyvinyl chloride passing through the first holes from the vinyl chloride wallpaper by rotating the first tubular portion in a state in which the vinyl chloride wallpaper shredded by the first shredding unit is accommodated in the first tubular portion, and an inside of the first tubular portion is provided with a rotating rod that has a central axis coinciding with a central axis of the first tubular portion and is rotatable about the central axis, and a screw member that is helically provided around the rotating rod and has a plurality of teeth formed in the screw member. a first shredding unit that shreds the vinyl chloride wallpaper; and a first separation unit that has a first tubular portion in which a large number of first holes that allow the polyvinyl chloride contained in the vinyl chloride wallpaper shredded by the first shredding unit to pass through without allowing the paper to pass through are formed, and that separates the polyvinyl chloride passing through the first holes from the vinyl chloride wallpaper by rotating the first tubular portion in a state in which the vinyl chloride wallpaper shredded by the first shredding unit is accommodated in the first tubular portion, and an inside of the first tubular portion is provided with a rotating rod that has a central axis coinciding with a central axis of the first tubular portion and is rotatable about the central axis, and a screw member that is helically provided around the rotating rod and has a plurality of teeth formed in the screw member.