2c represents an interval between the holding belt in a load path and the holding belt in a return path; A represents a depth to an arc top point of an outer peripheral surface of the guide groove in a direction change path; B represents a depth to an arc top point of an inner peripheral surface of the guide groove in the direction change path; “d” represents a thickness of the holding belt; and a=(A−d/2) and b=(B+d/2) are satisfied.