To exert a relatively strong magnetic force on the outflow position of engine oil and to surely remove metal powder mixed in the engine oil by providing a magnetic filtration device arranged in the chamber of a filter surrounded by a cylindrical metallic net through a base sheet to cover an oil outlet.

An oil inlet 201 and an oil outlet 202 are provided to the bottom face of the case 20 of an engine oil filter 2, and a cylindrical metallic net 204 is set in the case 20. A corrugated filter paper core 203 is interposed between the outer periphery of the net 204 and the inner periphery of the case 20, and the net 204 and core 203 are positioned and fixed by an elastic means 206. A magnetic filtration device 1 is furnished in the inside surrounded by the net 204 so as to cover the oil outlet 202 and formed by arranging an annular magnet 107 on the trapezoidal part 103 on a base sheet 10 having a repeatedly bent part 102, and the metal powder in the oil is attracted and removed by the strong magnetic force.