PURPOSE: To provide a strainer capable of attracting magnetic foreign matter by safely using a magnet element without damaging the same and capable of forcibly discharging the foreign matter caught by the magnet element and a screen to the outside without requiring disassembling and cleaning to certainly remove the same.

CONSTITUTION: A cylindrical screen 5 is arranged between the fluid inflow and outflow ports 2, 3 of a case and the foreign matter B contained in a fluid is caught by the screen 5. The base end part 21a of a sheath 21 composed of a non-magnetic material is supported within the case 1 in such a state that the screen 5 is inserted in the case 1. A magnet element 8 for attracting magnetic foreign matter A is arranged in the state inserted in the sheath 21 to be set so as to be movable between the position advancing toward the leading end of the sheath 21 and the position retreating toward the base end part 21a of the sheath 21. The discharge passage 31a of the foreign matters A, B is provided to the place near the base end part of the sheath 21 and opened and closed by a blow valve 33.