To firmly fix a filter member 5 to case members 6, 7 even if the dimensional management for a gap between filter member nipping surfaces 12, 13 in the case members 6, 7 and the management for the stroke amount in welding are comparatively gently performed in an oil strainer 1 formed by holding the filter member made of non-woven fabric between the paired case members 6, 7 and welding both case members to each other.

A projection 18 piercing the filter member 5 is provided on the filter member nipping surface 12 of one case member 7, and a hole 19 for storing the tip 18a of the projection 18 is provided in the filter member nipping surface 13 of the other case member 6. With the projection 18 pierced through the filter member 5 and the tip part 18a thereof stored in the hole 19, both case members 6, 7 are welded to each other.