To provide an oil filter which has an exchangeable filter part and prevents reduction of hydraulic pressure and oil film shortage caused by oil temperature rise by cooling the filtered oil through a cooling oil passage, in an automobile or a motorcycle adopting a cartridge-type oil filter.

A body base part 2 and a body case part 1 fixed to an oil filter attaching part by means of a fixation screw 3 can be split by detaching a flange connection fitting 5, for enabling exchange an inner filter part 4 alone. Contact area with oil is increased by arranging an oil passage 1 for cooling. The oil which flowed from an oil inlet 8 of a filter is cooled through the oil passage 11, filtered through the filter part 4, and made to flow out to the engine side from an oil outlet 9.