It is an object of the present invention to provide a filter for trapping foreign matter in which a filtration element can trap foreign matter that is admixed to a fluid present inside the filter with good reliability and a comparatively high trapping ratio. Hydraulic oil that has flown from an opening portion into a guide space of a first flow path guide is guided downward by the first flow path guide and directed toward a second flow path guide. As a result, the oil passes through a very narrow gap, that is, a gap with a cross sectional area of the flow path narrowed so as to increase the flow velocity of the hydraulic oil, a rising flow of the hydraulic oil is formed, and this flow is spouted up by the second flow path guide and guided by the first flow path guide toward a filter element. Foreign matter admixed to the hydraulic oil rises with good intensity together with the hydraulic oil and is moved by the hydraulic oil toward the filter element. Therefore, foreign matter can be trapped by the filter element with good reliability and a comparative high trapping ratio.