PURPOSE: To enable the simple and stable torque control of high accuracy to be performed by obtaining a deviation between the rotational position of a torque setting member and the elastic rotational position of a brake member due to torque reaction, relative with a fixing member, and applying a controlled variable corresponding to the deviation, to the control object element of the brake element.

CONSTITUTION: This electromagnetic retarder is equipped with a disc-like rotational member 11 coupled to the output rotational shaft 14 of a transmission, and a brake member 5 opposite thereto. The brake member 5 is so supported on a fixing member 12 as to be rotatable against a spring force, Many electromagnets 6 are supported on the brake member 5 in a peripheral direction, and so arranged that the poles of adjacent electromagnets 6 faced to the rotational member 11 are is made alternately different from each other. Also, a torque setting member 10 adjustable in rotation is supported on the fixing member 12, and the movable piece 10a of the aforesaid member 10 is kept in slidable contact with a circular arc variable resistor 7 laid on the brake member 5. Furthermore, a deviation between the rotational position of the torque setting member 10 and the elastic rotational position of the brake member 5 due to torque reaction, relative with the fixing member 12, is obtained, and a controlled variable corresponding to the deviation is applied to the electromagnets 6.