PURPOSE: To shorten a dimension in the direction of length by rationally arranging a Cardan joint by effectively utilizing a space between a gear box and a rear axle in a transmission including the gear box, the rear axle, and a double Cardan joint shaft.

CONSTITUTION: In a retarder including an induction stator 2 and an induction rotor 3 mounted in a cantilevered manner on an output part of a gear box 1, a coil ring 5 is held on a tubular flange 4 provided on the stator 2, and the flange 4 is attached to an intermediate beam mounting body 6 fixed on the gear box 1 through a spacer 7. On the other hand, two discs 9 made of a ferromagnetic material are provided on the rotor 3, and each disc 9 is attached to a ring 10 fixed on an intermediate annular body 13 integral with a gear box flange 14 by an arm 11 forming a ventilation fin. At this time, a Cardan joint 36 is fixed by utilizing an inner screw train 33 of the gear box flange 14, and a tubular insert 23 for attaching the intermediate annular body 13 is fixed by utilizing an outer screw train 44.