PURPOSE: To control formation of scale generated in a water supply pipe by passing water to be treated through a packed bed of ceramics irradiated by far-infrared rays and thereafter passing it between magnets forming a magnetic field.

CONSTITUTION: A water treating device is constituted by joining a magnetic field treatment part 3 to a ceramic treatment part 2 by a flange 1-2. Firstly, water to be treated enters a cylindrical vessel filling ceramic spheres through a perforated plate 7 and is brought into contact with the ceramic spheres to perform ceramic treatment. Then, water to be treated passes through the flange 1-2 and is delivered into the magnetic field treatment part 3. At this time, in the magnetic field treatment part 3, permanent magnets are fixed on at least one piece of fixture 6 parallel to the flow direction. Thereby, ceramic treatment and magnetic field treatment of water are continuously performed. Formation of scale generated in a water supply pipe is controlled.