PURPOSE: To prevent the scars on a seal from being deepened by the scars on a rod by reciprocating a seal holder with the fluid pressure applied to the seal holder and the energizing force of an energizing member, and rotating the seal holder via the coupling of a long hole and a pin.

CONSTITUTION: When pressure oil is fed to a chamber A on the right side of a piston 32 and the piston 32 is moved to the left, a seal holder 35 is moved to the right by the hydraulic force and retreated while compressing a rubber ball 44, and the seal holder 35 is rotated via the coupling of a pin 41 and a long hole 27. When pressure oil is fed to a chamber B on the left side of the piston 32 and the piston 32 is moved to the right, the pressure of the chamber A is low, the seal holder 35 is moved to the left by the elastic force of the rubber ball 44 and rotated via the coupling of the long hole 27 and the pin 41. When there are scars on the outer periphery of a rod 31, the range where scars are generated on a seal 38 is widened, however the depth of the scars is made shallow, and the occurrence of an oil leakage from the seal 38 is prevented.