PURPOSE: To make improvements in durability by setting up a partition wall forming member, partitioning the inside of a cylinder and a fluid passage, slidably in a partition wall storage space formed between the cylinder and the fluid passage.

CONSTITUTION: A partition wall storage space 24, housing a partition wall forming member 23 free of airtightly sliding motion, is formed in space between a fluid passage 12 and a cylinder 13 so as to be interconnected to the cylinder 13 where a plunger 14 is housed free of sliding motion. When this plunger 14 is reciprocatively slidden in the cylinder 13, lubricating oil in the cylinder 13 is subjected to high pressure, this pressure is transmitted to a ball type partition wall 25 of the partition wall forming member 23, this ball type partition wall 25 is slidden to the side of the fluid passage 12 in the partition wall storage space 24, and it pressurizes a fed fluid at the side of the fluid passage 12.