This paper proposes a method of simultaneously grasping multiple ropes together by a dual-armed robot, and as an application, achieves a bundling task by folding a rope. To grasp three or more ropes, we found that it is important to manipulate them so that the inner ropes float. Based on this finding, we designed a new grasping method. By repeated execution of the multiple-rope grasp, the task of bundling a long rope by folding them is achieved. Experiments showed the effectiveness of the proposed method.