PURPOSE: To minimize the speed fluctuation arising in a driven shaft with a driving device provided with two sets of universal joints by making the rotating phase of the 2nd driven shaft changeable.

CONSTITUTION: A platform 60 of a supporting device 62 is moved upward to support the 2nd universal joint 52 and face gears 48, 49 which are meshed with each other. The mounting bolts coupled on the central axis are removed. A hydraulic device is then operated to move the extending part of a driven shaft 36 to the driving source side along the axial direction, thereby disengaging the gears 48, 49 from each other. A driving is thereafter started to revolve the shaft 36 at an inching speed, by which the phase adjustment is easily performed. The easy setting of the phase adjustment between the 1st universal joint and the 2nd universal joint is thus made possible.