PURPOSE: To make a leakage of high pressure slurry outside preventable, by adjoining a feed chamber and a pressure chamber with a sealing device in between, while letting the high pressure slurry leaked from the sliding clearance of a plunger slide hole flow into the feed chamber.

CONSTITUTION: A feed chamber 3 and a pressure chamber 4 are adjoined close to each other with a sealing device 5 in between, while a plunger 6 is hermetically and slidably inserted through into a plunger slide hole 5a of the sealing device 5. Therefore, granting that high pressure slurry inside the pressure chamber 4 is leaked from a sliding clearance of the plunger slide hole 5a, this high pressure slurry flows in the inside of the feed chamber; in no case leaks outside, never. In addition, since at least a sliding surface part between the outer circumferential surface of the plunger 6 and the plunger slide hole 5a is constituted of a ceramic material, it is excellent in abrasion resistance so that highly superior pump performance is maintainable for a long period of time.