An electromagnetic type retarder comprises a main portion consisting of a stator having a plurality of magnetic coils arranged along a circle and spaced apart from one another, and of a steel rotor surrounding the stator and rotated according to the rotation of a tire; a driving device for the main portion to be controlled by an operation signal; and an output terminal for an additional device; the magnetic coils consisting of three-phase or two-phase connections. Each of the magnetic coils is connected with a capacitor so as to form a resonance circuit, respectively. The driving device has transistors connected in series to each of the connections and controlled so as to be opened and closed by the operation signal. The revolution speed of a rotary magnetic field generated by AC voltage induced in the magnetic coils forming the resonance circuits by the rotation of the steel rotor is set smaller than the revolution speed of the steel rotor. The AC voltage is applied to an input terminal of the additional device through a timer after a predetermined time from the generation of the operation signal.