Provided is a method for manufacturing a hollow-fiber-type blood processing device including a hollow fiber membrane bundle which is obtained by bundling a large number of hollow fiber membranes to have an outer shape formed in a cylindrical shape or a columnar shape, and a sheet body mounted on an outer peripheral portion of the hollow fiber membrane bundle. This manufacturing method has a mounting step of mounting the sheet body on the outer peripheral portion of the hollow fiber membrane bundle. When performing the mounting step, the sheet material is mounted in a state where the sheet material is previously formed as a cylindrical member. In addition, this sheet material is expandable, and the inner diameter of the sheet material in a case where the sheet material is in a cylindrical shape in a natural state where no external force is applied to the sheet material is smaller than the outer diameter of the hollow fiber membrane bundle.
