A device for manufacturing a fiber assembly includes: a rotating body that has a cylindrical shape, and winds and holds a plurality of support sheets around an outer peripheral surface around a rotation axis of the rotating body; a plurality of supply nozzles arranged along a direction parallel to the rotation axis, the supply nozzles supplying a polymer material to be a material of fibers to the plurality of support sheets; a supply nozzle moving unit that relatively moves the plurality of supply nozzles in the direction parallel to the rotation axis of the rotating body, in which the rotating body is rotatable about the rotation axis to wind, on main surfaces of the plurality of support sheets, fibers obtained by naturally cooling or naturally drying the polymer material supplied from the plurality of supply nozzles, and the rotating body includes a plurality of guide members in an annular shape circumscribing the outer peripheral surface of the rotating body concentrically to regulate positions of the plurality of support sheets.