PURPOSE: To enable movement of a body to be measured by applying a large force in a small space by a method wherein a pair of pistons equipped with piston rods to which elastic sleeves capable of holding the bar-shaped body to be measured are made to operate alternately by a pressure fluid.

CONSTITUTION: For the purpose of sending the body to be measured 6 into a furnace, the pressure fluid is injected into the hollow orifice 10 of the elastic sleeve 8 of a cylinder 4a and thereby the inside wall 11 thereof is swollen to the side of an insertion hole 9 to hold the body to be measured 6, while the pressure fluid in the hollow orifice 10 of the elastic sleeve 8 of the other cylinder 4b is discharged. Next, when the pressure fluid is injected from the port 19a of the cylinder 19a and the port 18b of the cylinder 4b, the piston 2 and the rod 3 of the cylinder 4a are moved to the left, holding still the measuring bar, while the rod of the cylinder 4b is moved to the right. By repeating the operation alternately, the body is sent into the furnace. Since the device is small, it requires no large space, and the body to be measured can be moved with a large force.