To restrain a magnetized inner ring from being dragged, in a protection bearing provided with a rolling element comprising a nonmagnetic substance.

The inner ring 41 and an outer ring 42 are formed of members each comprising a magnetic substance, and the rolling element 43 is formed of a nonmagnetic substance. A magnetic guide body 44 is a member formed of a magnetic material, and provided with a magnetic guide mechanism for guiding the magnetism of the magnetized inner ring to a closed magnetic path passing the inner ring and the outer ring. A magnetic guide part 44b is constituted of a portion overhung from the inner circumferential edge of a bearing fixing part 44a toward the extension direction of a bearing fixing part and an axial direction, and contacts with the outer ring to reduce magnetic resistance. A space of a clearance between the inner ring of the protection bearing and the magnetic guide part is constituted to be sufficiently small compared with a space of a clearance between the inner circumferential face of the inner ring and the outer circumferential wall face of a shaft 7. Many-pieces magnetic flux are picked up by providing the magnetic guide body to satisfy a relation of the space the space so as to be guided to the closed magnetic path passing the inner ring and the outer ring.