To provide a filter causing no lowering of flow speed of fluid at a connection part of a flow-in pipe with a vessel body.

This filter is provided with a vessel having a flow-out pipe 18 connected thereto and a filter basket 13 therein, a flow-in pipe 14 connected to an upper part of the vessel, and a drain pipe 15 connected to at least a lower part of the vessel, and fluid from the flow-in pipe 14 is filtered while being swirled like vortex in the vessel. A sectional area of the flow-in pipe 14 orthogonal to a centerline of the pipe 14 is set to be almost the same as an aperture area of an opening 11a of the vessel at a joint part J of the vessel with the flow-in pipe 14. A ratio of flow speed of fluid at the joint part J to that of fluid at the inlet of the flow-in pipe 14 is 0.9-1.1.