PURPOSE: To facilitate the inspection and replacement of an oil filter by arranging the oil filter in a filter chamber in a pump main body so that the oil filter is held by a removable cap closing the aperture of the filter chamber.

CONSTITUTION: A filter chamber 89 opening outward is formed near the bulkhead 73 of a pump main body 70, and the first through the third oil paths 83-85 are combined together in the filter chamber 89. An oil filter 90 is arranged in the filter chamber 89 so as to partition between the second oil path 84 provided with a suction valve 86 and the other first and third oil paths 83, 15, and the oil filter 90 is held by a removable cap 91 closing the aperture of the filter chamber 89. Therefore, the oil filter 90 can be easily inspected and replaced by removing the cap 91.