PURPOSE: To prevent malfunction or generation of reverse torque by connecting drive pinions on high and low speed sides and flexible shafts on high and low speed sides with a rigid coupling while performing the automatic interlock of scooping pipes through judging generation of a reverse torque based on both detected outputs of fluid couplings on high and low speed sides.

CONSTITUTION: Drive pinions 3a, 3b on high and low speed sides are rotated with increasing speed by a large drive gear 2 on a drive shaft 1 side, thereby flexible shafts 6a, 6b on high and low speed sides are connected to each other with rigid couplings 5a, 20 respectively so that, with a large centrifugal force due to increased speed of the couplings, the torque transmission between the pinions 3a, 3b and flexible shafts 6a, 6b are smoothly executed. In addition, the coupling outputs on the high and low speed sides are detected by high and output detectors on the high and low speed sides additionally provided on the fluid couplings (7a, 8a, 16a - 7b, 8b, 16b) on the high and low speed sides and the generation of a reverse torque is judged by comparing detected signals of respective coupling outputs in a controller, thus performing the automatic interlock of scooping pipes 15a, 15b on the high and low speed sides based on the control signal.