A magnetic field element includes magnetic field portions and a coupling portion and is rotatable on a rotation axis along a given direction. Each magnetic field portion includes a magnet and magnetic plates. The magnet includes first and second pole faces having different polarities from each other in the given direction. The magnetic-material plates are provided on the first and second pole faces. The magnetic field portions are annularly arranged along a circumferential direction around the rotation axis and spaced in the circumferential direction from one another. The coupling portion is made of a non-magnetic material and couples the magnetic field portions to one another.