PURPOSE: To simplify formation of a passage, by a method wherein a passage to intercommunicate pressure chambers is formed with a plurality of ports, formed in a body, and a communicating passage formed in a seal material.

CONSTITUTION: Axial ports 25 are formed in a pair of chambers 20a and 21a with which a pressure chamber 22A is formed, and axial ports 26 in a pair of chambers 20b and 21b with which a pressure chamber 22B is formed. A communication passage 35 is formed between O-rings 28 and 29, and a communicating passage 36 between O-rings 28. Thus, a passage to intercommunicate the chambers 20a and 21a can be formed with the port 25 and the communication passage 35, and a passage to intercommunicate the chambers 20b and 21b with the port 26 and the communication passage 36. This constitution enables extremely simple formation of a passage to intercommunicate a plurality of the chambers 20a, 20b, 21a and 21b, with which the pressure chambers 22A and 22B are formed.