An eddy current retarder, comprising: a cylindrical braking member that is fixed to a rotating shaft of a vehicle; a magnet retention member of a ferromagnetic material that is arranged inside the braking member, the magnet retention member retaining a plurality of magnets at regular intervals entirely in a circumferential direction such that the magnets face an inner peripheral surface of the braking member, wherein during braking the magnets and the braking member rotate with a relative rotational speed difference and eddy currents are induced in the braking member; and a brake switching mechanism that switches, during braking, to a state in which magnetic circuits develop between the magnets and the braking member, and switches, during non-braking, to a state in which no magnetic circuits develop, characterized in that the eddy current retarder additionally comprises an electricity generating function, wherein a plurality of protrusions or notch portions are provided on the braking member, wherein - in the case of protrusions, the plurality of protrusions are provided on an end face of the braking member in an axial direction at regular intervals entirely in the circumferential direction, and - in the case of notch portions, the plurality of notch portions are provided on an end portion of the braking member in an axial direction at regular intervals entirely in the circumferential direction, a plurality of electricity generating coils are provided in a non-rotating part of the vehicle at regular intervals entirely in the circumferential direction such that, - in the case of protrusions, the electricity generating coils face regions of the end face of the braking member where the protrusions are provided, and - in the case of notch portions, the electricity generating coils face regions of the end portion of the braking member where the notch portions are provided, from an outer peripheral surface side of the braking member, and during braking, positions of the magnets coincide with positions of the electricity generating coils in the circumferential direction, wherein magnetic fluxes repeatedly penetrate the electricity generating coils thereby causing induced currents to flow through the electricity generating coils to generate electricity. a cylindrical braking member that is fixed to a rotating shaft of a vehicle; a magnet retention member of a ferromagnetic material that is arranged inside the braking member, the magnet retention member retaining a plurality of magnets at regular intervals entirely in a circumferential direction such that the magnets face an inner peripheral surface of the braking member, wherein during braking the magnets and the braking member rotate with a relative rotational speed difference and eddy currents are induced in the braking member; and a brake switching mechanism that switches, during braking, to a state in which magnetic circuits develop between the magnets and the braking member, and switches, during non-braking, to a state in which no magnetic circuits develop, characterized in that the eddy current retarder additionally comprises an electricity generating function, wherein a plurality of protrusions or notch portions are provided on the braking member, wherein - in the case of protrusions, the plurality of protrusions are provided on an end face of the braking member in an axial direction at regular intervals entirely in the circumferential direction, and - in the case of notch portions, the plurality of notch portions are provided on an end portion of the braking member in an axial direction at regular intervals entirely in the circumferential direction, - in the case of protrusions, the plurality of protrusions are provided on an end face of the braking member in an axial direction at regular intervals entirely in the circumferential direction, and - in the case of notch portions, the plurality of notch portions are provided on an end portion of the braking member in an axial direction at regular intervals entirely in the circumferential direction, a plurality of electricity generating coils are provided in a non-rotating part of the vehicle at regular intervals entirely in the circumferential direction such that, - in the case of protrusions, the electricity generating coils face regions of the end face of the braking member where the protrusions are provided, and - in the case of notch portions, the electricity generating coils face regions of the end portion of the braking member where the notch portions are provided, from an outer peripheral surface side of the braking member, and - in the case of protrusions, the electricity generating coils face regions of the end face of the braking member where the protrusions are provided, and - in the case of notch portions, the electricity generating coils face regions of the end portion of the braking member where the notch portions are provided, from an outer peripheral surface side of the braking member, and during braking, positions of the magnets coincide with positions of the electricity generating coils in the circumferential direction, wherein magnetic fluxes repeatedly penetrate the electricity generating coils thereby causing induced currents to flow through the electricity generating coils to generate electricity.