A method of producing an opened fiber bundle is in a space-saving manner. The method of continuously producing an opened fiber bundle for a cleaning member, includes the steps of (a1) providing (i) first nip rolls, (ii) second nip rolls, (iii) third nip rolls, and (iv) an air feeder; (a2) conveying a fiber bundle using the first nip rolls and the second nip rolls to apply a tensile force to the fiber bundle; (a3) conveying the fiber bundle using the second nip rolls and the third nip rolls to relax the fiber bundle, thereby forming a belt-shaped fiber bundle; and (a4) blowing air from the air feeder in a direction intersecting with the conveying direction of the first belt-shaped fiber bundle.