PURPOSE: To average the strength of upper and lower couplings having an oval-shaped hole and to improve the strength of the oval-shaped hole parts by providing the phase of pivotally attaching part of cross pin of the upper and lower couplings having the oval-shaped hole shifting by a specified angle from the phases of the upper and lower oval-shaped holes.

CONSTITUTION: Upper and lower work rolls 2, 12 are crossed and revolved with upper and lower driving shafts 7, 17 through upper and lower couplings 6, 16, upper and lower universal joints 8, 9, 18, 19, upper and lower spindles 1, 11 and the upper and lower couplings 3, 13 having the oval-shaped hole. At this time, the phases of the upper and lower projecting parts 3a, 13a of the upper and lower couplings 3, 13 having the oval-shaped hole are shifted by about 45° from the phases of the oval-shaped holes. Then, the phase angle between the upper oval-shaped hole 3b and the pivotally attaching part of the cross pin 5 in the upper projecting part 3a and phase angle between the lower oval-shaped hole 13b and the pivotally attaching part of cross pin 5 in the lower projecting part 13a are approximately equalized. Consequently, strength drop due to approach of the thin wall part of the upper oval-shaped hole 3b to the pivotally attaching part of cross pin 5 in the upper projecting part 3a is evaded.