To realize the rapid quality control of a material by expanding a tube stock while an expanding jig is inserted in the tube stock to be tested, and measuring the contraction based on the length before and after the expansion of the tube stock to be tested to complete the test in a short time.

A tube stock 1 to be tested is inserted in an outer tube 2, the outer tube 2 is set to a protective tube 3, and an expanding rod 4 is advanced by operating a switching valve 8. An expanding brit 5 is advanced into the tube stock 1 to be tested to expand the tube. The expanding load is measured by a load cell 6, and the measured value is recorded in a recorder 7. When the expanding brit 5 reaches a stopper 9, the switching valve 8 is switched to reverse the expanding rod 4. The expanding contraction is obtained by the difference (L1-L1) between the measured value L1 of the tube stock 1 to be tested before the expansion and the measured value L2 after the expansion. Thus, one cycle from the preparation to the measurement of the contraction can be completed only in about five minutes, the test can be completed in a short time, and the quality of the material can be rapidly controlled.