PURPOSE: To greatly increase the quantity of attracted magnetic particles per unit area of filter elements, by making the numerous filter elements of ferrite-austenite steel and increasing the number of magnetic modules of each magnetic element.

CONSTITUTION: A cylindrical filter container 3 is made of non-magnetic material (e.g., aluminium) so that a fluid introduced through an inlet port 4 is conducted to an outlet port 6 through a filtering portion 5. Since the ferromagnetic austenite structure of each of the filter elements 10 filled in the filtering portion 5 is very fine one at micron order, the fine magnetic modules are magnetized and a very high magnetic field gradient is produced when magnetic field is applied to the filter elements. Therefore, the effective area for attraction of magnetic particles can be made very large. The magnetic particles contained in the fluid introduced throgh the inlet port 4 are attracted to the magnetic modules. Then, the fluid is drained through the outlet port 6