ELECTROMAGNETIC RETARDER

An electromagnetic type retarder having a main portion consisting of a stator having, a plurality of magnetic coils arranged along a circle and spaced apart from one another so as to form multi-phase connections, and of a steel rotor surrounding the stator and rotated according to the rotation of a tire; a control device; and a driving device consisting of at least two transistors opened and closed by a drive pulse from the control device, respectively. The multi phase connections are formed by the magnetic coils, the magnetic coils of each phase are connected with capacitors so as to form a resonance circuit, respectively, and each of the transistors is connected in series to at least two phase connections. The revolution speed of a rotary magnetic field induced in the magnetic coils by the rotation of the steel rotor is set smaller than the revolution speed of the steel rotor. A braking torque is controlled by turning ON and OFF the transistor inserted in one phase connection.