An eddy current retarder includes a brake drum, a magnet retention ring, and a switch mechanism. The brake drum is fixed to a rotating shaft. The magnet retention ring is arranged inside the drum and retains magnets at regular intervals entirely in a circumferential direction such that the magnets face the inner peripheral surface of the drum. The switch mechanism includes switch plates that switch, during braking, to a state in which magnetic circuits develop between the magnets and the drum, and switch, during non-braking, to a state in which no magnetic circuits develop. Protrusions are provided on an end face of the drum at regular intervals entirely in the circumferential direction. Electricity generating coils are provided in a non-rotating part of a vehicle at regular intervals entirely in the circumferential direction such that the electricity generating coils face the regions of the end face of the drum.