A method for producing a cable-sealing member is disclosed. The method comprises forming a formed rubber including a first plane and a second plane that oppose in a thickness direction and a side plane that bridges a peripheral edge of the first plane and a peripheral edge of the second plane. The method further includes rotating the formed rubber with one axis in the thickness direction as a rotary axis while a holder is applied over the side plane of the formed rubber and, meanwhile, inserting a cutting blade from the first plane into the formed rubber to form a ring-form slit portion and stopping the cutting blade just in front of the second plane, leaving a slit-form ring unbored on one side.