top chains 111 and the first bottom chain 112 and the other end of each columnar object 20 is sandwiched between the second top chain 115 and the second bottom chain 116 the motor 114 is used for driving the first top chain 111 the first bottom chain 112 the second top chain 115 and the second bottom chain 116 at a same speed to move in the first direction in other words the columnar objects 20 can move along with the operating unit 11 in the first direction no relative motion exists between the first top chain 111 and the first bottom chain 112 during the first top chain 111 and the first bottom chain 112 are driven to move in the first direction no relative motion exists between the second top 115 and the second bottom chain 116 during the second top chain 115 and the second bottom chain 116 are driven to move in the first direction in one embodiment the motor 114 can also drive the first holders 113 and the second holders 117 to rotate the columnar objects 20 at a same speed in another embodiment the first holders 113 and second holders 117 can be omitted the columnar objects 20 are fixed between the first top chain 111 and the first bottom chains 112 and are fixed between the second top chain 115 and the second bottom chain 116 the columnar objects 20 rotate by virtue of friction for example between the columnar objects 20.