PURPOSE: To enable concentration of the ends of through-holes to the end part of a rod, by a method wherein a plurality of through-holes are formed in the peripheral wall of a hollow rod along the direction of the axis of the rod, and the one end of the through-hole is opened on the one end side of the rod and communicated to a liquid chamber in a cylinder.

CONSTITUTION: Through-holes 41W43 are axially formed in a peripheral wall 40 of a hollow rod 3. The one end of each of the through-holes 41W43 opened on the one end 3a side of the rod 3 and facing a liquid chamber 17 in a cylinder 2, and the other end is opened on the end 3b side of the rod 3. Thereby, when working oil is injected in the liquid chamber 17, one out of the through-holes 41W43 is utilized. In this case, by escaping air in the cylinder 2 to the outside through the different through-hole, the liquid chamber 17 can be filled with liquid. An electric wire 51 connected to an actuator 35 is lead out from the end part of the rod 3 to the outside through the different through-hole. Since the through-holes 41W43 are axially formed in the peripheral wall 40 of the rod 3, their opening ends can be concentrated to the end part of the rod 3.