To treat fluid by allowing magnetic field, α ray and far-infrared rays to work on the fluid.

The fluid treating device 10 consists of a fluid pipe 11 consisting of a nonmagnetic member, permanent magnets 12a, 12b separately placed on the outside surface of the fluid pipe 11, and a sheet 13 for radiating α ray and far infrared rays, and magnetic field, α ray and far infrared rays are made to work on the fluid flowing in the inside of the fluid pipe 11. Thus, in the case that, for example, city water is passed through the inside of the fluid pipe 11, red rust in a city water pipe is removed and resticking of the rust is prevented.