PURPOSE: To enable measuring elongation of material very frequently and high temperature characteristic of a material exactly to be carried out by measuring the variation of the distance according to a jig mounting a weight directly connected with a sample piece on it, by using a laser length meter.

CONSTITUTION: In the center of a holder 2 embeded in the middle of a high temperature furnace mainbody 1, the top end of a sample piece 3 is fixed and at the bottom of the sample piece 3, a jig 5 having a disk 7 capable of mounting a weight is connected. Using a laser length meter 6 provided at the bottom of the mainbody 1, the distance from the standard plate 8 fixed planely on the disk 7 is measured and the measured signal is input in a personal computer to be stored and processed. By this, the elongation during a creep testing is frequently measured and recorded, and therefore, the variation of high temperature characteristic of a material, especially the elongation until break can be exactly measured and summing and analysis etc., become easy.